rounding to different amounts

a ppt is here

usually rounding to a finer amount (5p or 5c) will provide a more accurate estimate to the true cost than rounding to e.g. the nearest 10p or 10c
but not always...

for three addends:
rounding to the nearest 5p is more accurate in 123 cases
rounding to the nearest 10p is more accurate in 28 cases
and for the remaining 69 cases, both methods of rounding are equally accurate

for four addends:
nearest 5p = 417 cases
nearest 10p = 105 cases
equally accurate = 193 cases

for five addends:
nearest 5p = 1210 cases
nearest 10p = 321 cases
equally accurate = 471 cases

[thanks to the National Mathematics Project team, published in the UK in 1989, Eon Harper et al for these solutions and the suggestion for this task]