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	$246.61	11.722%	$275.5176	$275.52	$275.50	$275.50
Purchase #2	$20.58	8.785%	$22.388	$22.39	$22.40	$22.40
Purchase #3	$101.31	3.184%	$104.5357	$104.54	$104.55	$104.50
Purchase #4	$88.91	10.125%	$97.9121	$97.91	$97.90	$97.90
Purchase #5	$29.94	4.412%	$31.261	$31.26	$31.25	$31.30
Purchase #6	$177.53	7.275%	$190.4453	$190.45	$190.45	$190.40
Purchase #7	$45.72	8.111%	$49.4283	$49.43	$49.45	$49.40
7 purchase totals =	$710.60		$771.4880	$771.50	$771.50	$771.40