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	$123.72	4.203%	$128.92	$128.92	$128.90	$128.90
Purchase #2	$246.82	3.789%	$256.172	$256.17	$256.15	$256.20
Purchase #3	$210.29	10.730%	$232.8541	$232.85	$232.85	$232.90
Purchase #4	$60.84	10.731%	$67.3687	$67.37	$67.35	$67.40
Purchase #5	$221.83	11.334%	$246.9722	$246.97	$246.95	$247.00
Purchase #6	$220.68	9.287%	$241.1746	$241.17	$241.15	$241.20
Purchase #7	$76.67	7.734%	$82.5997	$82.60	$82.60	$82.60
7 purchase totals =	$1,160.85		$1,256.0613	$1,256.05	$1,255.95	$1,256.20