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	$199.88	11.826%	$223.5178	$223.52	$223.50	$223.50
Purchase #2	$192.93	9.118%	$210.5214	$210.52	$210.50	$210.50
Purchase #3	$133.29	8.614%	$144.7716	$144.77	$144.75	$144.80
Purchase #4	$238.55	10.575%	$263.7767	$263.78	$263.80	$263.80
Purchase #5	$137.91	6.344%	$146.659	$146.66	$146.65	$146.70
Purchase #6	$53.45	13.858%	$60.8571	$60.86	$60.85	$60.90
Purchase #7	$18.43	13.158%	$20.855	$20.86	$20.85	$20.90
7 purchase totals =	$974.44		$1,070.9586	$1,070.97	$1,070.90	$1,071.10