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	$65.57	11.168%	$72.8929	$72.89	$72.90	$72.90
Purchase #2	$133.54	6.451%	$142.1547	$142.15	$142.15	$142.20
Purchase #3	$244.93	4.490%	$255.9274	$255.93	$255.95	$255.90
Purchase #4	$88.59	8.277%	$95.9226	$95.92	$95.90	$95.90
Purchase #5	$88.42	13.565%	$100.4142	$100.41	$100.40	$100.40
Purchase #6	$11.83	6.275%	$12.5723	$12.57	$12.55	$12.60
Purchase #7	$201.76	3.409%	$208.638	$208.64	$208.65	$208.60
7 purchase totals =	$834.64		$888.5221	$888.51	$888.50	$888.50