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	$121.73	9.140%	$132.8561	$132.86	$132.85	$132.90
Purchase #2	$55.45	10.378%	$61.2046	$61.20	$61.20	$61.20
Purchase #3	$56.69	9.676%	$62.1753	$62.18	$62.20	$62.20
Purchase #4	$10.42	6.787%	$11.1272	$11.13	$11.15	$11.10
Purchase #5	$16.58	10.294%	$18.2867	$18.29	$18.30	$18.30
Purchase #6	$208.98	10.763%	$231.4725	$231.47	$231.45	$231.50
Purchase #7	$16.45	9.567%	$18.0238	$18.02	$18.00	$18.00
7 purchase totals =	$486.30		$535.1462	$535.15	$535.15	$535.20