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	$89.47	12.597%	$100.7405	$100.74	$100.75	$100.70
Purchase #2	$23.35	5.756%	$24.694	$24.69	$24.70	$24.70
Purchase #3	$108.38	10.578%	$119.8444	$119.84	$119.85	$119.80
Purchase #4	$55.65	6.316%	$59.1649	$59.16	$59.15	$59.20
Purchase #5	$56.32	11.752%	$62.9387	$62.94	$62.95	$62.90
Purchase #6	$188.79	13.308%	$213.9142	$213.91	$213.90	$213.90
Purchase #7	$218.61	3.167%	$225.5334	$225.53	$225.55	$225.50
7 purchase totals =	$740.57		$806.8301	$806.81	$806.85	$806.70