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	$75.32	4.250%	$78.5211	$78.52	$78.50	$78.50
Purchase #2	$246.32	3.749%	$255.5545	$255.55	$255.55	$255.60
Purchase #3	$240.87	10.347%	$265.7928	$265.79	$265.80	$265.80
Purchase #4	$153.85	13.632%	$174.8228	$174.82	$174.80	$174.80
Purchase #5	$52.83	5.472%	$55.7209	$55.72	$55.70	$55.70
Purchase #6	$249.83	11.719%	$279.1076	$279.11	$279.10	$279.10
Purchase #7	$180.29	11.602%	$201.2072	$201.21	$201.20	$201.20
7 purchase totals =	$1,199.31		$1,310.7269	$1,310.72	$1,310.65	$1,310.70