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	$122.53	6.436%	$130.416	$130.42	$130.40	$130.40
Purchase #2	$127.42	9.592%	$139.6421	$139.64	$139.65	$139.60
Purchase #3	$154.70	13.692%	$175.8815	$175.88	$175.90	$175.90
Purchase #4	$100.40	10.726%	$111.1689	$111.17	$111.15	$111.20
Purchase #5	$28.76	11.747%	$32.1384	$32.14	$32.15	$32.10
Purchase #6	$39.67	9.244%	$43.3371	$43.34	$43.35	$43.30
Purchase #7	$50.63	4.238%	$52.7757	$52.78	$52.80	$52.80
7 purchase totals =	$624.11		$685.3597	$685.37	$685.40	$685.30