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	$28.78	12.381%	$32.3433	$32.34	$32.35	$32.30
Purchase #2	$247.66	9.636%	$271.5245	$271.52	$271.50	$271.50
Purchase #3	$184.84	7.748%	$199.1614	$199.16	$199.15	$199.20
Purchase #4	$206.67	8.209%	$223.6355	$223.64	$223.65	$223.60
Purchase #5	$229.93	11.500%	$256.372	$256.37	$256.35	$256.40
Purchase #6	$113.80	9.351%	$124.4414	$124.44	$124.45	$124.40
Purchase #7	$17.72	12.208%	$19.8833	$19.88	$19.90	$19.90
7 purchase totals =	$1,029.40		$1,127.3614	$1,127.35	$1,127.35	$1,127.30