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	$50.93	3.111%	$52.5144	$52.51	$52.50	$52.50
Purchase #2	$52.38	10.171%	$57.7076	$57.71	$57.70	$57.70
Purchase #3	$60.61	11.385%	$67.5104	$67.51	$67.50	$67.50
Purchase #4	$61.46	9.693%	$67.4173	$67.42	$67.40	$67.40
Purchase #5	$203.86	10.405%	$225.0716	$225.07	$225.05	$225.10
Purchase #6	$70.70	7.160%	$75.7621	$75.76	$75.75	$75.80
Purchase #7	$56.81	11.306%	$63.2329	$63.23	$63.25	$63.20
7 purchase totals =	$556.75		$609.2163	$609.21	$609.15	$609.20