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	$11.87	6.743%	$12.6704	$12.67	$12.65	$12.70
Purchase #2	$208.78	11.700%	$233.2073	$233.21	$233.20	$233.20
Purchase #3	$224.48	11.500%	$250.2952	$250.30	$250.30	$250.30
Purchase #4	$86.70	8.290%	$93.8874	$93.89	$93.90	$93.90
Purchase #5	$157.33	9.772%	$172.7043	$172.70	$172.70	$172.70
Purchase #6	$181.65	7.286%	$194.885	$194.89	$194.90	$194.90
Purchase #7	$172.36	11.755%	$192.6209	$192.62	$192.60	$192.60
7 purchase totals =	$1,043.17		$1,150.2705	$1,150.28	$1,150.25	$1,150.30