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	$131.94	13.355%	$149.5606	$149.56	$149.55	$149.60
Purchase #2	$89.35	3.467%	$92.4478	$92.45	$92.45	$92.40
Purchase #3	$76.73	8.713%	$83.4155	$83.42	$83.40	$83.40
Purchase #4	$22.92	8.859%	$24.9505	$24.95	$24.95	$25.00
Purchase #5	$11.51	11.544%	$12.8387	$12.84	$12.85	$12.80
Purchase #6	$177.43	4.395%	$185.228	$185.23	$185.25	$185.20
Purchase #7	$98.52	13.494%	$111.8143	$111.81	$111.80	$111.80
7 purchase totals =	$608.40		$660.2554	$660.26	$660.25	$660.20