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	$148.50	7.549%	$159.7103	$159.71	$159.70	$159.70
Purchase #2	$88.73	12.201%	$99.5559	$99.56	$99.55	$99.60
Purchase #3	$172.66	10.248%	$190.3542	$190.35	$190.35	$190.40
Purchase #4	$93.65	9.576%	$102.6179	$102.62	$102.60	$102.60
Purchase #5	$32.82	13.767%	$37.3383	$37.34	$37.35	$37.30
Purchase #6	$25.83	10.157%	$28.4536	$28.45	$28.45	$28.50
Purchase #7	$239.51	13.476%	$271.7864	$271.79	$271.80	$271.80
7 purchase totals =	$801.70		$889.8166	$889.82	$889.80	$889.90