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	$47.84	11.382%	$53.2851	$53.29	$53.30	$53.30
Purchase #2	$50.85	3.319%	$52.5377	$52.54	$52.55	$52.50
Purchase #3	$206.81	13.701%	$235.145	$235.15	$235.15	$235.10
Purchase #4	$99.73	11.720%	$111.4184	$111.42	$111.40	$111.40
Purchase #5	$99.44	11.266%	$110.6429	$110.64	$110.65	$110.60
Purchase #6	$210.71	5.434%	$222.16	$222.16	$222.15	$222.20
Purchase #7	$88.25	12.487%	$99.2698	$99.27	$99.25	$99.30
7 purchase totals =	$803.63		$884.4589	$884.47	$884.45	$884.40