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	$168.97	6.805%	$180.4684	$180.47	$180.45	$180.50
Purchase #2	$37.57	13.134%	$42.5044	$42.50	$42.50	$42.50
Purchase #3	$216.50	13.741%	$246.2493	$246.25	$246.25	$246.20
Purchase #4	$55.88	3.292%	$57.7196	$57.72	$57.70	$57.70
Purchase #5	$206.29	7.143%	$221.0253	$221.03	$221.05	$221.00
Purchase #6	$127.89	12.147%	$143.4248	$143.42	$143.40	$143.40
Purchase #7	$44.83	5.612%	$47.3459	$47.35	$47.35	$47.30
7 purchase totals =	$857.93		$938.7377	$938.74	$938.70	$938.60