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	$244.96	4.798%	$256.7132	$256.71	$256.70	$256.70
Purchase #2	$99.59	6.184%	$105.7486	$105.75	$105.75	$105.70
Purchase #3	$81.78	7.426%	$87.853	$87.85	$87.85	$87.90
Purchase #4	$59.35	3.518%	$61.4379	$61.44	$61.45	$61.40
Purchase #5	$82.79	7.155%	$88.7136	$88.71	$88.70	$88.70
Purchase #6	$22.99	12.659%	$25.9003	$25.90	$25.90	$25.90
Purchase #7	$38.27	4.107%	$39.8417	$39.84	$39.85	$39.80
7 purchase totals =	$629.73		$666.2083	$666.20	$666.20	$666.10