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	$19.89	13.820%	$22.6388	$22.64	$22.65	$22.60
Purchase #2	$160.85	11.795%	$179.8223	$179.82	$179.80	$179.80
Purchase #3	$149.60	5.556%	$157.9118	$157.91	$157.90	$157.90
Purchase #4	$197.71	9.467%	$216.4272	$216.43	$216.45	$216.40
Purchase #5	$45.69	6.181%	$48.5141	$48.51	$48.50	$48.50
Purchase #6	$242.85	11.275%	$270.2313	$270.23	$270.25	$270.20
Purchase #7	$67.37	6.763%	$71.9262	$71.93	$71.95	$71.90
7 purchase totals =	$883.96		$967.4717	$967.47	$967.50	$967.30