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	$223.75	13.767%	$254.5537	$254.55	$254.55	$254.60
Purchase #2	$164.34	12.325%	$184.5949	$184.59	$184.60	$184.60
Purchase #3	$103.41	7.537%	$111.204	$111.20	$111.20	$111.20
Purchase #4	$148.41	7.394%	$159.3834	$159.38	$159.40	$159.40
Purchase #5	$59.26	8.245%	$64.146	$64.15	$64.15	$64.10
Purchase #6	$34.53	7.340%	$37.0645	$37.06	$37.05	$37.10
Purchase #7	$85.68	7.276%	$91.9141	$91.91	$91.90	$91.90
7 purchase totals =	$819.38		$902.8606	$902.84	$902.85	$902.90