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	$46.52	8.490%	$50.4695	$50.47	$50.45	$50.50
Purchase #2	$140.29	4.450%	$146.5329	$146.53	$146.55	$146.50
Purchase #3	$48.47	7.106%	$51.9143	$51.91	$51.90	$51.90
Purchase #4	$250.68	10.157%	$276.1416	$276.14	$276.15	$276.10
Purchase #5	$110.91	12.314%	$124.5675	$124.57	$124.55	$124.60
Purchase #6	$182.71	7.476%	$196.3694	$196.37	$196.35	$196.40
Purchase #7	$141.96	7.159%	$152.1229	$152.12	$152.10	$152.10
7 purchase totals =	$921.54		$998.1181	$998.11	$998.05	$998.10