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	$83.58	8.717%	$90.8657	$90.87	$90.85	$90.90
Purchase #2	$95.50	5.524%	$100.7754	$100.78	$100.80	$100.80
Purchase #3	$145.40	9.325%	$158.9586	$158.96	$158.95	$159.00
Purchase #4	$72.48	7.707%	$78.066	$78.07	$78.05	$78.10
Purchase #5	$131.44	8.548%	$142.6755	$142.68	$142.70	$142.70
Purchase #6	$55.75	3.468%	$57.6834	$57.68	$57.70	$57.70
Purchase #7	$59.67	11.193%	$66.3489	$66.35	$66.35	$66.30
7 purchase totals =	$643.82		$695.3735	$695.39	$695.40	$695.50