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	$146.88	12.700%	$165.5338	$165.53	$165.55	$165.50
Purchase #2	$154.60	4.467%	$161.506	$161.51	$161.50	$161.50
Purchase #3	$169.94	13.467%	$192.8258	$192.83	$192.85	$192.80
Purchase #4	$40.69	3.358%	$42.0564	$42.06	$42.05	$42.10
Purchase #5	$90.69	5.487%	$95.6662	$95.67	$95.65	$95.70
Purchase #6	$44.59	9.229%	$48.7052	$48.71	$48.70	$48.70
Purchase #7	$195.89	10.613%	$216.6798	$216.68	$216.70	$216.70
7 purchase totals =	$843.28		$922.9732	$922.99	$923.00	$923.00