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	$235.86	8.264%	$255.3515	$255.35	$255.35	$255.40
Purchase #2	$149.39	10.320%	$164.807	$164.81	$164.80	$164.80
Purchase #3	$76.95	7.505%	$82.7251	$82.73	$82.75	$82.70
Purchase #4	$180.91	5.863%	$191.5168	$191.52	$191.50	$191.50
Purchase #5	$12.56	8.286%	$13.6007	$13.60	$13.60	$13.60
Purchase #6	$178.61	3.320%	$184.5399	$184.54	$184.55	$184.50
Purchase #7	$75.72	11.223%	$84.2181	$84.22	$84.20	$84.20
7 purchase totals =	$910.00		$976.7591	$976.77	$976.75	$976.70