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	$50.61	7.459%	$54.385	$54.39	$54.40	$54.40
Purchase #2	$139.65	8.442%	$151.4393	$151.44	$151.45	$151.40
Purchase #3	$117.74	10.411%	$129.9979	$130.00	$130.00	$130.00
Purchase #4	$40.56	7.409%	$43.5651	$43.57	$43.55	$43.60
Purchase #5	$86.76	9.753%	$95.2217	$95.22	$95.20	$95.20
Purchase #6	$9.79	6.764%	$10.4522	$10.45	$10.45	$10.50
Purchase #7	$108.27	3.347%	$111.8938	$111.89	$111.90	$111.90
7 purchase totals =	$553.38		$596.9550	$596.96	$596.95	$597.00