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	$165.51	12.283%	$185.8396	$185.84	$185.85	$185.80
Purchase #2	$108.33	9.589%	$118.7178	$118.72	$118.70	$118.70
Purchase #3	$36.55	11.594%	$40.7876	$40.79	$40.80	$40.80
Purchase #4	$170.88	4.516%	$178.5969	$178.60	$178.60	$178.60
Purchase #5	$141.47	7.205%	$151.6629	$151.66	$151.65	$151.70
Purchase #6	$24.32	12.343%	$27.3218	$27.32	$27.30	$27.30
Purchase #7	$248.51	4.874%	$260.6224	$260.62	$260.60	$260.60
7 purchase totals =	$895.57		$963.5490	$963.55	$963.50	$963.50