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	$80.56	12.707%	$90.7968	$90.80	$90.80	$90.80
Purchase #2	$203.46	12.136%	$228.1519	$228.15	$228.15	$228.20
Purchase #3	$92.51	13.141%	$104.6667	$104.67	$104.65	$104.70
Purchase #4	$229.77	12.775%	$259.1231	$259.12	$259.10	$259.10
Purchase #5	$199.96	7.487%	$214.931	$214.93	$214.95	$214.90
Purchase #6	$33.93	10.521%	$37.4998	$37.50	$37.50	$37.50
Purchase #7	$74.40	3.319%	$76.8693	$76.87	$76.85	$76.90
7 purchase totals =	$914.59		$1,012.0386	$1,012.04	$1,012.00	$1,012.10