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	$79.51	12.548%	$89.4869	$89.49	$89.50	$89.50
Purchase #2	$147.70	8.249%	$159.8838	$159.88	$159.90	$159.90
Purchase #3	$47.92	12.334%	$53.8305	$53.83	$53.85	$53.80
Purchase #4	$198.64	11.733%	$221.9464	$221.95	$221.95	$221.90
Purchase #5	$31.83	10.155%	$35.0623	$35.06	$35.05	$35.10
Purchase #6	$215.71	4.690%	$225.8268	$225.83	$225.85	$225.80
Purchase #7	$105.36	11.486%	$117.4616	$117.46	$117.45	$117.50
7 purchase totals =	$826.67		$903.4983	$903.50	$903.55	$903.50