Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.84	8.799%	$92.3051	$92.31	$92.30	$92.30
Purchase #2	$45.55	6.259%	$48.401	$48.40	$48.40	$48.40
Purchase #3	$45.61	7.194%	$48.8912	$48.89	$48.90	$48.90
Purchase #4	$124.73	9.375%	$136.4234	$136.42	$136.40	$136.40
Purchase #5	$120.57	5.705%	$127.4485	$127.45	$127.45	$127.40
Purchase #6	$224.38	3.241%	$231.6522	$231.65	$231.65	$231.70
Purchase #7	$246.51	9.258%	$269.3319	$269.33	$269.35	$269.30
7 purchase totals =	$892.19		$954.4533	$954.45	$954.45	$954.40