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	$137.87	7.563%	$148.2971	$148.30	$148.30	$148.30
Purchase #2	$91.89	12.584%	$103.4534	$103.45	$103.45	$103.50
Purchase #3	$63.54	3.243%	$65.6006	$65.60	$65.60	$65.60
Purchase #4	$105.47	4.334%	$110.0411	$110.04	$110.05	$110.00
Purchase #5	$37.87	11.846%	$42.3561	$42.36	$42.35	$42.40
Purchase #6	$186.97	12.733%	$210.7769	$210.78	$210.80	$210.80
Purchase #7	$135.49	7.761%	$146.0054	$146.01	$146.00	$146.00
7 purchase totals =	$759.10		$826.5306	$826.54	$826.55	$826.60