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	$24.62	3.617%	$25.5105	$25.51	$25.50	$25.50
Purchase #2	$33.28	9.541%	$36.4552	$36.46	$36.45	$36.50
Purchase #3	$128.96	11.859%	$144.2534	$144.25	$144.25	$144.30
Purchase #4	$146.42	8.168%	$158.3796	$158.38	$158.40	$158.40
Purchase #5	$111.35	6.866%	$118.9953	$119.00	$119.00	$119.00
Purchase #6	$170.54	5.294%	$179.5684	$179.57	$179.55	$179.60
Purchase #7	$83.88	13.514%	$95.2155	$95.22	$95.20	$95.20
7 purchase totals =	$699.05		$758.3779	$758.39	$758.35	$758.50