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	$169.57	12.457%	$190.6933	$190.69	$190.70	$190.70
Purchase #2	$137.43	4.552%	$143.6858	$143.69	$143.70	$143.70
Purchase #3	$10.88	9.179%	$11.8787	$11.88	$11.90	$11.90
Purchase #4	$10.87	7.188%	$11.6513	$11.65	$11.65	$11.70
Purchase #5	$102.76	13.164%	$116.2873	$116.29	$116.30	$116.30
Purchase #6	$93.46	4.707%	$97.8592	$97.86	$97.85	$97.90
Purchase #7	$92.28	3.620%	$95.6205	$95.62	$95.60	$95.60
7 purchase totals =	$617.25		$667.6761	$667.68	$667.70	$667.80