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	$129.85	12.797%	$146.4669	$146.47	$146.45	$146.50
Purchase #2	$47.61	11.444%	$53.0585	$53.06	$53.05	$53.10
Purchase #3	$184.44	10.330%	$203.4927	$203.49	$203.50	$203.50
Purchase #4	$124.77	10.484%	$137.8509	$137.85	$137.85	$137.90
Purchase #5	$70.35	10.207%	$77.5306	$77.53	$77.55	$77.50
Purchase #6	$105.50	8.388%	$114.3493	$114.35	$114.35	$114.30
Purchase #7	$34.83	7.338%	$37.3858	$37.39	$37.40	$37.40
7 purchase totals =	$697.35		$770.1347	$770.14	$770.15	$770.20