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	$72.56	13.246%	$82.1713	$82.17	$82.15	$82.20
Purchase #2	$141.55	6.402%	$150.612	$150.61	$150.60	$150.60
Purchase #3	$148.60	10.793%	$164.6384	$164.64	$164.65	$164.60
Purchase #4	$101.58	9.347%	$111.0747	$111.07	$111.05	$111.10
Purchase #5	$15.86	4.257%	$16.5352	$16.54	$16.55	$16.50
Purchase #6	$85.37	11.152%	$94.8905	$94.89	$94.90	$94.90
Purchase #7	$137.34	8.518%	$149.0386	$149.04	$149.05	$149.00
7 purchase totals =	$702.86		$768.9607	$768.96	$768.95	$768.90