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	$149.64	6.672%	$159.624	$159.62	$159.60	$159.60
Purchase #2	$195.40	8.114%	$211.2548	$211.25	$211.25	$211.30
Purchase #3	$6.79	12.379%	$7.6305	$7.63	$7.65	$7.60
Purchase #4	$159.59	8.131%	$172.5663	$172.57	$172.55	$172.60
Purchase #5	$187.72	11.660%	$209.6082	$209.61	$209.60	$209.60
Purchase #6	$108.33	10.634%	$119.8498	$119.85	$119.85	$119.80
Purchase #7	$189.47	8.643%	$205.8459	$205.85	$205.85	$205.80
7 purchase totals =	$996.94		$1,086.3795	$1,086.38	$1,086.35	$1,086.30