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	$64.66	12.709%	$72.8776	$72.88	$72.90	$72.90
Purchase #2	$113.65	5.429%	$119.8201	$119.82	$119.80	$119.80
Purchase #3	$76.80	7.309%	$82.4133	$82.41	$82.40	$82.40
Purchase #4	$233.85	10.666%	$258.7924	$258.79	$258.80	$258.80
Purchase #5	$36.35	11.503%	$40.5313	$40.53	$40.55	$40.50
Purchase #6	$32.74	8.333%	$35.4682	$35.47	$35.45	$35.50
Purchase #7	$9.29	3.278%	$9.5945	$9.59	$9.60	$9.60
7 purchase totals =	$567.34		$619.4974	$619.49	$619.50	$619.50