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	$130.85	11.821%	$146.3178	$146.32	$146.30	$146.30
Purchase #2	$181.83	8.299%	$196.9201	$196.92	$196.90	$196.90
Purchase #3	$201.69	13.147%	$228.2062	$228.21	$228.20	$228.20
Purchase #4	$224.70	12.869%	$253.6166	$253.62	$253.60	$253.60
Purchase #5	$244.85	13.497%	$277.8974	$277.90	$277.90	$277.90
Purchase #6	$146.85	13.602%	$166.8245	$166.82	$166.80	$166.80
Purchase #7	$6.31	13.407%	$7.156	$7.16	$7.15	$7.20
7 purchase totals =	$1,137.08		$1,276.9386	$1,276.95	$1,276.85	$1,276.90