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	$188.36	11.214%	$209.4827	$209.48	$209.50	$209.50
Purchase #2	$37.93	7.652%	$40.8324	$40.83	$40.85	$40.80
Purchase #3	$248.88	9.580%	$272.7227	$272.72	$272.70	$272.70
Purchase #4	$37.71	12.545%	$42.4407	$42.44	$42.45	$42.40
Purchase #5	$154.29	4.163%	$160.7131	$160.71	$160.70	$160.70
Purchase #6	$246.99	11.574%	$275.5766	$275.58	$275.60	$275.60
Purchase #7	$232.53	10.224%	$256.3039	$256.30	$256.30	$256.30
7 purchase totals =	$1,146.69		$1,258.0721	$1,258.06	$1,258.10	$1,258.00