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	$57.78	13.362%	$65.5006	$65.50	$65.50	$65.50
Purchase #2	$146.58	8.257%	$158.6831	$158.68	$158.70	$158.70
Purchase #3	$67.92	13.513%	$77.098	$77.10	$77.10	$77.10
Purchase #4	$27.49	10.281%	$30.3162	$30.32	$30.30	$30.30
Purchase #5	$137.45	6.253%	$146.0447	$146.04	$146.05	$146.00
Purchase #6	$24.77	12.357%	$27.8308	$27.83	$27.85	$27.80
Purchase #7	$93.61	6.332%	$99.5374	$99.54	$99.55	$99.50
7 purchase totals =	$555.60		$605.0108	$605.01	$605.05	$604.90