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	$87.58	5.194%	$92.1289	$92.13	$92.15	$92.10
Purchase #2	$128.82	8.422%	$139.6692	$139.67	$139.65	$139.70
Purchase #3	$31.27	9.846%	$34.3488	$34.35	$34.35	$34.30
Purchase #4	$91.68	8.521%	$99.4921	$99.49	$99.50	$99.50
Purchase #5	$33.70	11.724%	$37.651	$37.65	$37.65	$37.70
Purchase #6	$156.51	6.448%	$166.6018	$166.60	$166.60	$166.60
Purchase #7	$235.63	6.493%	$250.9295	$250.93	$250.95	$250.90
7 purchase totals =	$765.19		$820.8213	$820.82	$820.85	$820.80