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	$40.53	11.719%	$45.2797	$45.28	$45.30	$45.30
Purchase #2	$55.42	7.518%	$59.5865	$59.59	$59.60	$59.60
Purchase #3	$124.78	11.455%	$139.0735	$139.07	$139.05	$139.10
Purchase #4	$142.32	10.167%	$156.7897	$156.79	$156.80	$156.80
Purchase #5	$214.54	5.317%	$225.9471	$225.95	$225.95	$225.90
Purchase #6	$134.77	9.136%	$147.0826	$147.08	$147.10	$147.10
Purchase #7	$172.85	6.563%	$184.1941	$184.19	$184.20	$184.20
7 purchase totals =	$885.21		$957.9532	$957.95	$958.00	$958.00