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	$209.69	3.703%	$217.4548	$217.45	$217.45	$217.50
Purchase #2	$95.45	9.689%	$104.6982	$104.70	$104.70	$104.70
Purchase #3	$238.76	10.372%	$263.5242	$263.52	$263.50	$263.50
Purchase #4	$20.45	3.332%	$21.1314	$21.13	$21.15	$21.10
Purchase #5	$90.50	5.755%	$95.7083	$95.71	$95.70	$95.70
Purchase #6	$87.53	13.371%	$99.2336	$99.23	$99.25	$99.20
Purchase #7	$108.85	4.304%	$113.5349	$113.53	$113.55	$113.50
7 purchase totals =	$851.23		$915.2854	$915.27	$915.30	$915.20