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	$151.51	9.349%	$165.6747	$165.67	$165.65	$165.70
Purchase #2	$33.68	10.474%	$37.2076	$37.21	$37.20	$37.20
Purchase #3	$227.46	12.610%	$256.1427	$256.14	$256.15	$256.10
Purchase #4	$10.48	3.631%	$10.8605	$10.86	$10.85	$10.90
Purchase #5	$175.37	4.324%	$182.953	$182.95	$182.95	$183.00
Purchase #6	$192.58	7.275%	$206.5902	$206.59	$206.60	$206.60
Purchase #7	$83.52	8.709%	$90.7938	$90.79	$90.80	$90.80
7 purchase totals =	$874.60		$950.2225	$950.21	$950.20	$950.30