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	$171.62	9.845%	$188.516	$188.52	$188.50	$188.50
Purchase #2	$106.91	8.850%	$116.3715	$116.37	$116.35	$116.40
Purchase #3	$136.29	11.688%	$152.2196	$152.22	$152.20	$152.20
Purchase #4	$37.56	5.813%	$39.7434	$39.74	$39.75	$39.70
Purchase #5	$41.60	9.539%	$45.5682	$45.57	$45.55	$45.60
Purchase #6	$90.89	8.650%	$98.752	$98.75	$98.75	$98.80
Purchase #7	$71.65	6.789%	$76.5143	$76.51	$76.50	$76.50
7 purchase totals =	$656.52		$717.6850	$717.68	$717.60	$717.70