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	$104.93	11.619%	$117.1218	$117.12	$117.10	$117.10
Purchase #2	$161.75	8.719%	$175.853	$175.85	$175.85	$175.90
Purchase #3	$199.25	12.254%	$223.6661	$223.67	$223.65	$223.70
Purchase #4	$196.58	4.744%	$205.9058	$205.91	$205.90	$205.90
Purchase #5	$155.93	10.330%	$172.0376	$172.04	$172.05	$172.00
Purchase #6	$219.67	5.261%	$231.2268	$231.23	$231.25	$231.20
Purchase #7	$158.93	3.461%	$164.4306	$164.43	$164.45	$164.40
7 purchase totals =	$1,197.04		$1,290.2417	$1,290.25	$1,290.25	$1,290.20