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	$9.44	11.371%	$10.5134	$10.51	$10.50	$10.50
Purchase #2	$41.31	3.126%	$42.6014	$42.60	$42.60	$42.60
Purchase #3	$211.36	8.213%	$228.719	$228.72	$228.70	$228.70
Purchase #4	$237.47	9.687%	$260.4737	$260.47	$260.45	$260.50
Purchase #5	$20.27	7.361%	$21.7621	$21.76	$21.75	$21.80
Purchase #6	$18.66	10.799%	$20.6751	$20.68	$20.70	$20.70
Purchase #7	$55.51	10.588%	$61.3874	$61.39	$61.40	$61.40
7 purchase totals =	$594.02		$646.1321	$646.13	$646.10	$646.20