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	$59.71	10.151%	$65.7712	$65.77	$65.75	$65.80
Purchase #2	$40.34	12.808%	$45.5067	$45.51	$45.50	$45.50
Purchase #3	$151.88	13.325%	$172.118	$172.12	$172.10	$172.10
Purchase #4	$189.86	3.353%	$196.226	$196.23	$196.25	$196.20
Purchase #5	$107.96	9.252%	$117.9485	$117.95	$117.95	$117.90
Purchase #6	$120.95	8.281%	$130.9659	$130.97	$130.95	$131.00
Purchase #7	$184.68	5.489%	$194.8171	$194.82	$194.80	$194.80
7 purchase totals =	$855.38		$923.3534	$923.37	$923.30	$923.30