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	$209.33	6.155%	$222.2143	$222.21	$222.20	$222.20
Purchase #2	$159.99	9.469%	$175.1395	$175.14	$175.15	$175.10
Purchase #3	$55.87	10.112%	$61.5196	$61.52	$61.50	$61.50
Purchase #4	$164.97	4.550%	$172.4761	$172.48	$172.50	$172.50
Purchase #5	$61.78	8.204%	$66.8484	$66.85	$66.85	$66.80
Purchase #6	$18.67	5.308%	$19.661	$19.66	$19.65	$19.70
Purchase #7	$145.98	8.706%	$158.689	$158.69	$158.70	$158.70
7 purchase totals =	$816.59		$876.5479	$876.55	$876.55	$876.50