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	$170.53	12.153%	$191.2545	$191.25	$191.25	$191.30
Purchase #2	$57.55	13.406%	$65.2652	$65.27	$65.25	$65.30
Purchase #3	$40.35	12.716%	$45.4809	$45.48	$45.50	$45.50
Purchase #4	$55.48	8.184%	$60.0205	$60.02	$60.00	$60.00
Purchase #5	$118.65	5.769%	$125.4949	$125.49	$125.50	$125.50
Purchase #6	$171.70	7.810%	$185.1098	$185.11	$185.10	$185.10
Purchase #7	$136.38	11.195%	$151.6477	$151.65	$151.65	$151.60
7 purchase totals =	$750.64		$824.2735	$824.27	$824.25	$824.30