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	$60.56	9.405%	$66.2557	$66.26	$66.25	$66.30
Purchase #2	$217.41	6.528%	$231.6025	$231.60	$231.60	$231.60
Purchase #3	$56.46	6.559%	$60.1632	$60.16	$60.15	$60.20
Purchase #4	$6.78	12.392%	$7.6202	$7.62	$7.60	$7.60
Purchase #5	$18.81	8.153%	$20.3436	$20.34	$20.35	$20.30
Purchase #6	$223.48	11.688%	$249.6003	$249.60	$249.60	$249.60
Purchase #7	$38.44	11.144%	$42.7238	$42.72	$42.70	$42.70
7 purchase totals =	$621.94		$678.3093	$678.30	$678.25	$678.30