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	$75.51	12.737%	$85.1277	$85.13	$85.15	$85.10
Purchase #2	$139.40	10.430%	$153.9394	$153.94	$153.95	$153.90
Purchase #3	$62.93	13.721%	$71.5646	$71.56	$71.55	$71.60
Purchase #4	$12.26	8.613%	$13.316	$13.32	$13.30	$13.30
Purchase #5	$82.59	5.531%	$87.1581	$87.16	$87.15	$87.20
Purchase #6	$77.37	10.678%	$85.6316	$85.63	$85.65	$85.60
Purchase #7	$95.70	5.117%	$100.597	$100.60	$100.60	$100.60
7 purchase totals =	$545.76		$597.3344	$597.34	$597.35	$597.30