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	$93.40	6.816%	$99.7661	$99.77	$99.75	$99.80
Purchase #2	$178.47	12.456%	$200.7002	$200.70	$200.70	$200.70
Purchase #3	$77.80	7.679%	$83.7743	$83.77	$83.75	$83.80
Purchase #4	$151.90	10.413%	$167.7173	$167.72	$167.70	$167.70
Purchase #5	$78.84	5.332%	$83.0437	$83.04	$83.05	$83.00
Purchase #6	$178.96	11.484%	$199.5118	$199.51	$199.50	$199.50
Purchase #7	$140.60	11.699%	$157.0488	$157.05	$157.05	$157.00
7 purchase totals =	$899.97		$991.5622	$991.56	$991.50	$991.50