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	$220.48	13.570%	$250.3991	$250.40	$250.40	$250.40
Purchase #2	$231.35	12.121%	$259.3919	$259.39	$259.40	$259.40
Purchase #3	$229.35	7.617%	$246.8196	$246.82	$246.80	$246.80
Purchase #4	$155.28	11.324%	$172.8639	$172.86	$172.85	$172.90
Purchase #5	$64.74	3.487%	$66.9975	$67.00	$67.00	$67.00
Purchase #6	$102.52	8.784%	$111.5254	$111.53	$111.55	$111.50
Purchase #7	$142.93	12.650%	$161.0106	$161.01	$161.00	$161.00
7 purchase totals =	$1,146.65		$1,269.0080	$1,269.01	$1,269.00	$1,269.00