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	$120.37	8.455%	$130.5473	$130.55	$130.55	$130.50
Purchase #2	$122.98	4.778%	$128.856	$128.86	$128.85	$128.90
Purchase #3	$70.65	9.789%	$77.5659	$77.57	$77.55	$77.60
Purchase #4	$87.29	12.693%	$98.3697	$98.37	$98.35	$98.40
Purchase #5	$79.73	10.681%	$88.246	$88.25	$88.25	$88.20
Purchase #6	$50.66	5.684%	$53.5395	$53.54	$53.55	$53.50
Purchase #7	$247.52	3.580%	$256.3812	$256.38	$256.40	$256.40
7 purchase totals =	$779.20		$833.5056	$833.52	$833.50	$833.50