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	$230.96	10.787%	$255.8737	$255.87	$255.85	$255.90
Purchase #2	$93.67	13.630%	$106.4372	$106.44	$106.45	$106.40
Purchase #3	$110.45	12.743%	$124.5246	$124.52	$124.50	$124.50
Purchase #4	$137.91	12.679%	$155.3956	$155.40	$155.40	$155.40
Purchase #5	$129.45	13.391%	$146.7846	$146.78	$146.80	$146.80
Purchase #6	$54.76	8.505%	$59.4173	$59.42	$59.40	$59.40
Purchase #7	$95.55	9.674%	$104.7935	$104.79	$104.80	$104.80
7 purchase totals =	$852.75		$953.2265	$953.22	$953.20	$953.20