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	$227.85	13.480%	$258.5642	$258.56	$258.55	$258.60
Purchase #2	$35.93	11.484%	$40.0562	$40.06	$40.05	$40.10
Purchase #3	$151.70	10.490%	$167.6133	$167.61	$167.60	$167.60
Purchase #4	$130.65	10.611%	$144.5133	$144.51	$144.50	$144.50
Purchase #5	$229.97	6.758%	$245.5114	$245.51	$245.50	$245.50
Purchase #6	$40.34	11.340%	$44.9146	$44.91	$44.90	$44.90
Purchase #7	$120.95	13.658%	$137.4694	$137.47	$137.45	$137.50
7 purchase totals =	$937.39		$1,038.6424	$1,038.63	$1,038.55	$1,038.70