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	$228.38	12.335%	$256.5507	$256.55	$256.55	$256.60
Purchase #2	$219.97	9.601%	$241.0893	$241.09	$241.10	$241.10
Purchase #3	$37.82	13.220%	$42.8198	$42.82	$42.80	$42.80
Purchase #4	$53.52	9.228%	$58.4588	$58.46	$58.45	$58.50
Purchase #5	$38.63	9.667%	$42.3644	$42.36	$42.35	$42.40
Purchase #6	$175.41	8.546%	$190.4005	$190.40	$190.40	$190.40
Purchase #7	$45.66	11.419%	$50.8739	$50.87	$50.85	$50.90
7 purchase totals =	$799.39		$882.5574	$882.55	$882.50	$882.70