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	$99.34	13.346%	$112.5979	$112.60	$112.60	$112.60
Purchase #2	$146.30	3.837%	$151.9135	$151.91	$151.90	$151.90
Purchase #3	$77.81	4.676%	$81.4484	$81.45	$81.45	$81.40
Purchase #4	$72.54	7.766%	$78.1735	$78.17	$78.15	$78.20
Purchase #5	$221.87	4.779%	$232.4732	$232.47	$232.45	$232.50
Purchase #6	$234.61	5.439%	$247.3704	$247.37	$247.35	$247.40
Purchase #7	$75.85	5.691%	$80.1666	$80.17	$80.15	$80.20
7 purchase totals =	$928.32		$984.1435	$984.14	$984.05	$984.20