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	$130.62	6.547%	$139.1717	$139.17	$139.15	$139.20
Purchase #2	$236.81	5.288%	$249.3325	$249.33	$249.35	$249.30
Purchase #3	$70.29	10.571%	$77.7204	$77.72	$77.70	$77.70
Purchase #4	$201.96	9.777%	$221.7056	$221.71	$221.70	$221.70
Purchase #5	$196.72	13.560%	$223.3952	$223.40	$223.40	$223.40
Purchase #6	$160.85	3.151%	$165.9184	$165.92	$165.90	$165.90
Purchase #7	$11.89	10.733%	$13.1662	$13.17	$13.15	$13.20
7 purchase totals =	$1,009.14		$1,090.4100	$1,090.42	$1,090.35	$1,090.40