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	$135.80	4.430%	$141.8159	$141.82	$141.80	$141.80
Purchase #2	$153.58	12.130%	$172.2093	$172.21	$172.20	$172.20
Purchase #3	$147.37	5.358%	$155.2661	$155.27	$155.25	$155.30
Purchase #4	$123.47	6.832%	$131.9055	$131.91	$131.90	$131.90
Purchase #5	$149.87	13.387%	$169.9331	$169.93	$169.95	$169.90
Purchase #6	$37.40	4.555%	$39.1036	$39.10	$39.10	$39.10
Purchase #7	$187.25	12.353%	$210.381	$210.38	$210.40	$210.40
7 purchase totals =	$934.74		$1,020.6145	$1,020.62	$1,020.60	$1,020.60