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	$40.39	11.783%	$45.1492	$45.15	$45.15	$45.10
Purchase #2	$62.91	13.624%	$71.4809	$71.48	$71.50	$71.50
Purchase #3	$137.78	9.697%	$151.1405	$151.14	$151.15	$151.10
Purchase #4	$111.63	5.676%	$117.9661	$117.97	$117.95	$118.00
Purchase #5	$70.78	6.601%	$75.4522	$75.45	$75.45	$75.50
Purchase #6	$100.27	9.228%	$109.5229	$109.52	$109.50	$109.50
Purchase #7	$224.60	11.414%	$250.2358	$250.24	$250.25	$250.20
7 purchase totals =	$748.36		$820.9476	$820.95	$820.95	$820.90