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	$39.35	12.629%	$44.3195	$44.32	$44.30	$44.30
Purchase #2	$216.53	11.581%	$241.6063	$241.61	$241.60	$241.60
Purchase #3	$158.70	3.690%	$164.556	$164.56	$164.55	$164.60
Purchase #4	$135.96	10.707%	$150.5172	$150.52	$150.50	$150.50
Purchase #5	$135.66	8.286%	$146.9008	$146.90	$146.90	$146.90
Purchase #6	$30.36	5.541%	$32.0422	$32.04	$32.05	$32.00
Purchase #7	$197.30	9.795%	$216.6255	$216.63	$216.65	$216.60
7 purchase totals =	$913.86		$996.5675	$996.58	$996.55	$996.50