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	$92.43	12.264%	$103.7656	$103.77	$103.75	$103.80
Purchase #2	$83.47	8.378%	$90.4631	$90.46	$90.45	$90.50
Purchase #3	$131.97	12.844%	$148.9202	$148.92	$148.90	$148.90
Purchase #4	$129.62	12.738%	$146.131	$146.13	$146.15	$146.10
Purchase #5	$21.75	10.555%	$24.0457	$24.05	$24.05	$24.00
Purchase #6	$93.47	13.217%	$105.8239	$105.82	$105.80	$105.80
Purchase #7	$233.39	6.153%	$247.7505	$247.75	$247.75	$247.80
7 purchase totals =	$786.10		$866.9000	$866.90	$866.85	$866.90