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	$47.99	10.692%	$53.1211	$53.12	$53.10	$53.10
Purchase #2	$37.33	12.742%	$42.0866	$42.09	$42.10	$42.10
Purchase #3	$236.51	5.762%	$250.1377	$250.14	$250.15	$250.10
Purchase #4	$151.65	3.746%	$157.3308	$157.33	$157.35	$157.30
Purchase #5	$46.86	4.223%	$48.8389	$48.84	$48.85	$48.80
Purchase #6	$208.55	13.377%	$236.4477	$236.45	$236.45	$236.40
Purchase #7	$203.71	5.487%	$214.8876	$214.89	$214.90	$214.90
7 purchase totals =	$932.60		$1,002.8504	$1,002.86	$1,002.90	$1,002.70