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	$208.56	12.319%	$234.2525	$234.25	$234.25	$234.30
Purchase #2	$10.37	8.466%	$11.2479	$11.25	$11.25	$11.20
Purchase #3	$146.95	12.670%	$165.5686	$165.57	$165.55	$165.60
Purchase #4	$19.62	11.625%	$21.9008	$21.90	$21.90	$21.90
Purchase #5	$41.52	9.579%	$45.4972	$45.50	$45.50	$45.50
Purchase #6	$19.68	8.597%	$21.3719	$21.37	$21.35	$21.40
Purchase #7	$40.60	12.792%	$45.7936	$45.79	$45.80	$45.80
7 purchase totals =	$487.30		$545.6325	$545.63	$545.60	$545.70