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	$26.43	7.414%	$28.3895	$28.39	$28.40	$28.40
Purchase #2	$242.74	3.104%	$250.2746	$250.27	$250.25	$250.30
Purchase #3	$126.94	10.252%	$139.9539	$139.95	$139.95	$140.00
Purchase #4	$126.40	3.562%	$130.9024	$130.90	$130.90	$130.90
Purchase #5	$33.70	10.536%	$37.2506	$37.25	$37.25	$37.30
Purchase #6	$196.36	10.823%	$217.612	$217.61	$217.60	$217.60
Purchase #7	$145.83	13.614%	$165.6833	$165.68	$165.70	$165.70
7 purchase totals =	$898.40		$970.0663	$970.05	$970.05	$970.20