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	$45.42	8.507%	$49.2839	$49.28	$49.30	$49.30
Purchase #2	$215.47	12.690%	$242.8131	$242.81	$242.80	$242.80
Purchase #3	$57.71	11.735%	$64.4823	$64.48	$64.50	$64.50
Purchase #4	$219.49	5.527%	$231.6212	$231.62	$231.60	$231.60
Purchase #5	$30.71	6.700%	$32.7676	$32.77	$32.75	$32.80
Purchase #6	$55.39	11.622%	$61.8274	$61.83	$61.85	$61.80
Purchase #7	$59.92	10.266%	$66.0714	$66.07	$66.05	$66.10
7 purchase totals =	$684.11		$748.8669	$748.86	$748.85	$748.90