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	$213.42	3.845%	$221.626	$221.63	$221.65	$221.60
Purchase #2	$100.63	7.672%	$108.3503	$108.35	$108.35	$108.40
Purchase #3	$208.48	9.789%	$228.8881	$228.89	$228.90	$228.90
Purchase #4	$194.83	6.870%	$208.2148	$208.21	$208.20	$208.20
Purchase #5	$36.57	7.355%	$39.2597	$39.26	$39.25	$39.30
Purchase #6	$53.39	4.706%	$55.9025	$55.90	$55.90	$55.90
Purchase #7	$126.75	11.533%	$141.3681	$141.37	$141.35	$141.40
7 purchase totals =	$934.07		$1,003.6095	$1,003.61	$1,003.60	$1,003.70