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	$44.39	13.427%	$50.3502	$50.35	$50.35	$50.40
Purchase #2	$52.59	5.598%	$55.534	$55.53	$55.55	$55.50
Purchase #3	$18.37	13.785%	$20.9023	$20.90	$20.90	$20.90
Purchase #4	$15.77	13.863%	$17.9562	$17.96	$17.95	$18.00
Purchase #5	$84.51	4.796%	$88.5631	$88.56	$88.55	$88.60
Purchase #6	$217.66	12.210%	$244.2363	$244.24	$244.25	$244.20
Purchase #7	$74.43	7.801%	$80.2363	$80.24	$80.25	$80.20
7 purchase totals =	$507.72		$557.7784	$557.78	$557.80	$557.80