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	$11.26	5.764%	$11.909	$11.91	$11.90	$11.90
Purchase #2	$91.63	9.588%	$100.4155	$100.42	$100.40	$100.40
Purchase #3	$119.52	6.161%	$126.8836	$126.88	$126.90	$126.90
Purchase #4	$40.58	12.106%	$45.4926	$45.49	$45.50	$45.50
Purchase #5	$231.36	4.145%	$240.9499	$240.95	$240.95	$240.90
Purchase #6	$131.53	9.599%	$144.1556	$144.16	$144.15	$144.20
Purchase #7	$60.97	8.796%	$66.3329	$66.33	$66.35	$66.30
7 purchase totals =	$686.85		$736.1391	$736.14	$736.15	$736.10