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	$204.55	4.405%	$213.5604	$213.56	$213.55	$213.60
Purchase #2	$87.73	13.621%	$99.6797	$99.68	$99.70	$99.70
Purchase #3	$29.82	8.687%	$32.4105	$32.41	$32.40	$32.40
Purchase #4	$48.65	12.162%	$54.5668	$54.57	$54.55	$54.60
Purchase #5	$232.59	9.773%	$255.321	$255.32	$255.30	$255.30
Purchase #6	$248.44	12.680%	$279.9422	$279.94	$279.95	$279.90
Purchase #7	$52.99	7.112%	$56.7586	$56.76	$56.75	$56.80
7 purchase totals =	$904.77		$992.2392	$992.24	$992.20	$992.30