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	$152.91	4.331%	$159.5325	$159.53	$159.55	$159.50
Purchase #2	$72.57	12.203%	$81.4257	$81.43	$81.45	$81.40
Purchase #3	$32.52	7.277%	$34.8865	$34.89	$34.90	$34.90
Purchase #4	$72.67	9.538%	$79.6013	$79.60	$79.60	$79.60
Purchase #5	$189.90	11.525%	$211.786	$211.79	$211.80	$211.80
Purchase #6	$140.98	3.657%	$146.1356	$146.14	$146.15	$146.10
Purchase #7	$106.70	4.246%	$111.2305	$111.23	$111.25	$111.20
7 purchase totals =	$768.25		$824.5981	$824.61	$824.70	$824.50