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	$50.58	10.341%	$55.8105	$55.81	$55.80	$55.80
Purchase #2	$17.85	8.632%	$19.3908	$19.39	$19.40	$19.40
Purchase #3	$41.29	10.643%	$45.6845	$45.68	$45.70	$45.70
Purchase #4	$36.55	10.374%	$40.3417	$40.34	$40.35	$40.30
Purchase #5	$77.79	13.616%	$88.3819	$88.38	$88.40	$88.40
Purchase #6	$181.61	9.152%	$198.2309	$198.23	$198.25	$198.20
Purchase #7	$130.25	12.559%	$146.6081	$146.61	$146.60	$146.60
7 purchase totals =	$535.92		$594.4484	$594.44	$594.50	$594.40