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	$209.90	13.782%	$238.8284	$238.83	$238.85	$238.80
Purchase #2	$82.77	7.210%	$88.7377	$88.74	$88.75	$88.70
Purchase #3	$216.30	11.298%	$240.7376	$240.74	$240.75	$240.70
Purchase #4	$127.25	12.732%	$143.4515	$143.45	$143.45	$143.50
Purchase #5	$182.35	10.163%	$200.8822	$200.88	$200.90	$200.90
Purchase #6	$92.72	13.786%	$105.5024	$105.50	$105.50	$105.50
Purchase #7	$221.97	11.819%	$248.2046	$248.20	$248.20	$248.20
7 purchase totals =	$1,133.26		$1,266.3444	$1,266.34	$1,266.40	$1,266.30