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	$74.35	12.422%	$83.5858	$83.59	$83.60	$83.60
Purchase #2	$37.43	13.336%	$42.4217	$42.42	$42.40	$42.40
Purchase #3	$250.54	8.660%	$272.2368	$272.24	$272.25	$272.20
Purchase #4	$83.88	8.263%	$90.811	$90.81	$90.80	$90.80
Purchase #5	$52.92	10.555%	$58.5057	$58.51	$58.50	$58.50
Purchase #6	$52.85	11.245%	$58.793	$58.79	$58.80	$58.80
Purchase #7	$57.90	5.669%	$61.1824	$61.18	$61.20	$61.20
7 purchase totals =	$609.87		$667.5364	$667.54	$667.55	$667.50