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	$144.37	12.141%	$161.898	$161.90	$161.90	$161.90
Purchase #2	$110.81	12.251%	$124.3853	$124.39	$124.40	$124.40
Purchase #3	$183.59	9.226%	$200.528	$200.53	$200.55	$200.50
Purchase #4	$61.77	8.301%	$66.8975	$66.90	$66.90	$66.90
Purchase #5	$204.93	9.822%	$225.0582	$225.06	$225.05	$225.10
Purchase #6	$214.40	8.157%	$231.8886	$231.89	$231.90	$231.90
Purchase #7	$40.67	12.325%	$45.6826	$45.68	$45.70	$45.70
7 purchase totals =	$960.54		$1,056.3382	$1,056.35	$1,056.40	$1,056.40