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	$129.71	11.389%	$144.4827	$144.48	$144.50	$144.50
Purchase #2	$153.39	4.394%	$160.13	$160.13	$160.15	$160.10
Purchase #3	$59.44	10.459%	$65.6568	$65.66	$65.65	$65.70
Purchase #4	$114.63	10.198%	$126.32	$126.32	$126.30	$126.30
Purchase #5	$9.26	9.760%	$10.1638	$10.16	$10.15	$10.20
Purchase #6	$106.90	8.753%	$116.257	$116.26	$116.25	$116.30
Purchase #7	$50.50	7.171%	$54.1214	$54.12	$54.10	$54.10
7 purchase totals =	$623.83		$677.1317	$677.13	$677.10	$677.20