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	$248.89	4.526%	$260.1548	$260.15	$260.15	$260.20
Purchase #2	$33.99	11.201%	$37.7972	$37.80	$37.80	$37.80
Purchase #3	$244.52	8.217%	$264.6122	$264.61	$264.60	$264.60
Purchase #4	$137.71	3.200%	$142.1167	$142.12	$142.10	$142.10
Purchase #5	$40.44	11.853%	$45.2334	$45.23	$45.25	$45.20
Purchase #6	$41.54	10.853%	$46.0483	$46.05	$46.05	$46.00
Purchase #7	$22.45	10.425%	$24.7904	$24.79	$24.80	$24.80
7 purchase totals =	$769.54		$820.7530	$820.75	$820.75	$820.70