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	$206.89	12.105%	$231.934	$231.93	$231.95	$231.90
Purchase #2	$250.30	3.518%	$259.1056	$259.11	$259.10	$259.10
Purchase #3	$17.41	10.362%	$19.214	$19.21	$19.20	$19.20
Purchase #4	$29.69	7.200%	$31.8277	$31.83	$31.85	$31.80
Purchase #5	$208.67	4.547%	$218.1582	$218.16	$218.15	$218.20
Purchase #6	$136.82	4.472%	$142.9386	$142.94	$142.95	$142.90
Purchase #7	$143.62	5.756%	$151.8868	$151.89	$151.90	$151.90
7 purchase totals =	$993.40		$1,055.0649	$1,055.07	$1,055.10	$1,055.00