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	$190.57	12.230%	$213.8767	$213.88	$213.90	$213.90
Purchase #2	$49.34	11.808%	$55.1661	$55.17	$55.15	$55.20
Purchase #3	$246.70	11.189%	$274.3033	$274.30	$274.30	$274.30
Purchase #4	$241.33	5.460%	$254.5066	$254.51	$254.50	$254.50
Purchase #5	$126.43	3.783%	$131.2128	$131.21	$131.20	$131.20
Purchase #6	$16.71	11.314%	$18.6006	$18.60	$18.60	$18.60
Purchase #7	$38.82	10.497%	$42.8949	$42.89	$42.90	$42.90
7 purchase totals =	$909.90		$990.5610	$990.56	$990.55	$990.60