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	$42.43	12.476%	$47.7236	$47.72	$47.70	$47.70
Purchase #2	$84.89	4.276%	$88.5199	$88.52	$88.50	$88.50
Purchase #3	$11.86	10.593%	$13.1163	$13.12	$13.10	$13.10
Purchase #4	$94.64	13.267%	$107.1959	$107.20	$107.20	$107.20
Purchase #5	$142.49	12.156%	$159.8111	$159.81	$159.80	$159.80
Purchase #6	$46.62	12.626%	$52.5062	$52.51	$52.50	$52.50
Purchase #7	$33.59	12.259%	$37.7078	$37.71	$37.70	$37.70
7 purchase totals =	$456.52		$506.5808	$506.59	$506.50	$506.50