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	$83.29	8.810%	$90.6278	$90.63	$90.65	$90.60
Purchase #2	$155.29	7.122%	$166.3498	$166.35	$166.35	$166.30
Purchase #3	$56.76	5.699%	$59.9948	$59.99	$60.00	$60.00
Purchase #4	$172.47	10.761%	$191.0295	$191.03	$191.05	$191.00
Purchase #5	$34.86	3.322%	$36.018	$36.02	$36.00	$36.00
Purchase #6	$27.84	11.867%	$31.1438	$31.14	$31.15	$31.10
Purchase #7	$228.51	12.182%	$256.3471	$256.35	$256.35	$256.30
7 purchase totals =	$759.02		$831.5108	$831.51	$831.55	$831.30