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	$62.41	6.277%	$66.3275	$66.33	$66.35	$66.30
Purchase #2	$219.53	12.518%	$247.0108	$247.01	$247.00	$247.00
Purchase #3	$139.86	9.161%	$152.6726	$152.67	$152.65	$152.70
Purchase #4	$65.56	12.297%	$73.6219	$73.62	$73.60	$73.60
Purchase #5	$83.86	4.738%	$87.8333	$87.83	$87.85	$87.80
Purchase #6	$90.98	13.137%	$102.932	$102.93	$102.95	$102.90
Purchase #7	$169.73	5.757%	$179.5014	$179.50	$179.50	$179.50
7 purchase totals =	$831.93		$909.8995	$909.89	$909.90	$909.80