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	$89.40	12.634%	$100.6948	$100.69	$100.70	$100.70
Purchase #2	$63.29	5.644%	$66.8621	$66.86	$66.85	$66.90
Purchase #3	$72.35	8.121%	$78.2255	$78.23	$78.25	$78.20
Purchase #4	$154.25	12.666%	$173.7873	$173.79	$173.80	$173.80
Purchase #5	$218.64	7.760%	$235.6065	$235.61	$235.60	$235.60
Purchase #6	$13.78	6.783%	$14.7147	$14.71	$14.70	$14.70
Purchase #7	$158.43	7.213%	$169.8576	$169.86	$169.85	$169.90
7 purchase totals =	$770.14		$839.7485	$839.75	$839.75	$839.80