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	$113.98	13.622%	$129.5064	$129.51	$129.50	$129.50
Purchase #2	$143.80	11.673%	$160.5858	$160.59	$160.60	$160.60
Purchase #3	$17.33	12.291%	$19.46	$19.46	$19.45	$19.50
Purchase #4	$65.63	10.151%	$72.2921	$72.29	$72.30	$72.30
Purchase #5	$121.97	7.338%	$130.9202	$130.92	$130.90	$130.90
Purchase #6	$84.67	7.258%	$90.8153	$90.82	$90.80	$90.80
Purchase #7	$31.99	3.733%	$33.1842	$33.18	$33.20	$33.20
7 purchase totals =	$579.37		$636.7640	$636.77	$636.75	$636.80