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	$172.99	11.381%	$192.678	$192.68	$192.70	$192.70
Purchase #2	$95.96	4.860%	$100.6237	$100.62	$100.60	$100.60
Purchase #3	$220.51	4.476%	$230.38	$230.38	$230.40	$230.40
Purchase #4	$230.54	11.225%	$256.4181	$256.42	$256.40	$256.40
Purchase #5	$65.65	3.447%	$67.913	$67.91	$67.90	$67.90
Purchase #6	$230.74	12.318%	$259.1626	$259.16	$259.15	$259.20
Purchase #7	$206.80	7.669%	$222.6595	$222.66	$222.65	$222.70
7 purchase totals =	$1,223.19		$1,329.8349	$1,329.83	$1,329.80	$1,329.90