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	$80.77	11.817%	$90.3146	$90.31	$90.30	$90.30
Purchase #2	$208.94	13.576%	$237.3057	$237.31	$237.30	$237.30
Purchase #3	$37.68	7.105%	$40.3572	$40.36	$40.35	$40.40
Purchase #4	$139.89	7.410%	$150.2558	$150.26	$150.25	$150.30
Purchase #5	$140.94	7.577%	$151.619	$151.62	$151.60	$151.60
Purchase #6	$226.29	8.510%	$245.5473	$245.55	$245.55	$245.50
Purchase #7	$189.70	3.167%	$195.7078	$195.71	$195.70	$195.70
7 purchase totals =	$1,024.21		$1,111.1074	$1,111.12	$1,111.05	$1,111.10