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	$228.91	12.316%	$257.1026	$257.10	$257.10	$257.10
Purchase #2	$137.56	4.697%	$144.0212	$144.02	$144.00	$144.00
Purchase #3	$128.30	8.693%	$139.4531	$139.45	$139.45	$139.50
Purchase #4	$110.60	11.696%	$123.5358	$123.54	$123.55	$123.50
Purchase #5	$136.74	13.308%	$154.9374	$154.94	$154.95	$154.90
Purchase #6	$166.49	3.386%	$172.1274	$172.13	$172.15	$172.10
Purchase #7	$32.46	6.309%	$34.5079	$34.51	$34.50	$34.50
7 purchase totals =	$941.06		$1,025.6854	$1,025.69	$1,025.70	$1,025.60