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	$223.59	11.874%	$250.1391	$250.14	$250.15	$250.10
Purchase #2	$134.83	9.661%	$147.8559	$147.86	$147.85	$147.90
Purchase #3	$10.91	12.103%	$12.2304	$12.23	$12.25	$12.20
Purchase #4	$67.58	6.858%	$72.2146	$72.21	$72.20	$72.20
Purchase #5	$137.63	7.850%	$148.434	$148.43	$148.45	$148.40
Purchase #6	$58.96	4.503%	$61.615	$61.62	$61.60	$61.60
Purchase #7	$176.92	4.385%	$184.6779	$184.68	$184.70	$184.70
7 purchase totals =	$810.42		$877.1669	$877.17	$877.20	$877.10