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	$44.85	7.380%	$48.1599	$48.16	$48.15	$48.20
Purchase #2	$140.57	10.332%	$155.0937	$155.09	$155.10	$155.10
Purchase #3	$133.28	6.259%	$141.622	$141.62	$141.60	$141.60
Purchase #4	$22.29	10.392%	$24.6064	$24.61	$24.60	$24.60
Purchase #5	$121.25	4.120%	$126.2455	$126.25	$126.25	$126.20
Purchase #6	$35.95	4.624%	$37.6123	$37.61	$37.60	$37.60
Purchase #7	$123.95	6.671%	$132.2187	$132.22	$132.20	$132.20
7 purchase totals =	$622.14		$665.5585	$665.56	$665.50	$665.50