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	$88.37	12.717%	$99.608	$99.61	$99.60	$99.60
Purchase #2	$195.48	13.733%	$222.3253	$222.33	$222.35	$222.30
Purchase #3	$160.72	11.780%	$179.6528	$179.65	$179.65	$179.70
Purchase #4	$165.26	8.370%	$179.0923	$179.09	$179.10	$179.10
Purchase #5	$103.53	11.213%	$115.1388	$115.14	$115.15	$115.10
Purchase #6	$145.59	4.511%	$152.1576	$152.16	$152.15	$152.20
Purchase #7	$223.38	9.851%	$245.3852	$245.39	$245.40	$245.40
7 purchase totals =	$1,082.33		$1,193.3600	$1,193.37	$1,193.40	$1,193.40