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	$50.39	6.190%	$53.5091	$53.51	$53.50	$53.50
Purchase #2	$192.29	4.370%	$200.6931	$200.69	$200.70	$200.70
Purchase #3	$149.52	13.671%	$169.9609	$169.96	$169.95	$170.00
Purchase #4	$139.90	4.714%	$146.4949	$146.49	$146.50	$146.50
Purchase #5	$178.38	12.325%	$200.3653	$200.37	$200.35	$200.40
Purchase #6	$190.31	8.689%	$206.846	$206.85	$206.85	$206.80
Purchase #7	$34.68	13.807%	$39.4683	$39.47	$39.45	$39.50
7 purchase totals =	$935.47		$1,017.3376	$1,017.34	$1,017.30	$1,017.40