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	$34.88	7.863%	$37.6226	$37.62	$37.60	$37.60
Purchase #2	$55.37	13.586%	$62.8926	$62.89	$62.90	$62.90
Purchase #3	$157.72	7.513%	$169.5695	$169.57	$169.55	$169.60
Purchase #4	$42.68	9.182%	$46.5989	$46.60	$46.60	$46.60
Purchase #5	$152.90	10.264%	$168.5937	$168.59	$168.60	$168.60
Purchase #6	$119.52	7.501%	$128.4852	$128.49	$128.50	$128.50
Purchase #7	$55.90	9.660%	$61.2999	$61.30	$61.30	$61.30
7 purchase totals =	$618.97		$675.0624	$675.06	$675.05	$675.10