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	$192.93	13.389%	$218.7614	$218.76	$218.75	$218.80
Purchase #2	$242.34	12.165%	$271.8207	$271.82	$271.80	$271.80
Purchase #3	$53.50	13.279%	$60.6043	$60.60	$60.60	$60.60
Purchase #4	$212.82	13.105%	$240.7101	$240.71	$240.70	$240.70
Purchase #5	$105.62	5.474%	$111.4016	$111.40	$111.40	$111.40
Purchase #6	$55.34	7.111%	$59.2752	$59.28	$59.30	$59.30
Purchase #7	$171.52	7.672%	$184.679	$184.68	$184.70	$184.70
7 purchase totals =	$1,034.07		$1,147.2523	$1,147.25	$1,147.25	$1,147.30