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	$28.81	13.304%	$32.6429	$32.64	$32.65	$32.60
Purchase #2	$43.79	4.358%	$45.6984	$45.70	$45.70	$45.70
Purchase #3	$209.70	10.405%	$231.5193	$231.52	$231.50	$231.50
Purchase #4	$193.95	12.230%	$217.6701	$217.67	$217.65	$217.70
Purchase #5	$139.58	5.739%	$147.5905	$147.59	$147.60	$147.60
Purchase #6	$64.59	11.451%	$71.9862	$71.99	$72.00	$72.00
Purchase #7	$216.96	7.672%	$233.6052	$233.61	$233.60	$233.60
7 purchase totals =	$897.38		$980.7126	$980.72	$980.70	$980.70