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	$12.45	3.498%	$12.8855	$12.89	$12.90	$12.90
Purchase #2	$244.91	3.390%	$253.2124	$253.21	$253.20	$253.20
Purchase #3	$78.80	8.161%	$85.2309	$85.23	$85.25	$85.20
Purchase #4	$18.69	8.810%	$20.3366	$20.34	$20.35	$20.30
Purchase #5	$180.45	6.627%	$192.4084	$192.41	$192.40	$192.40
Purchase #6	$117.85	12.537%	$132.6249	$132.62	$132.60	$132.60
Purchase #7	$127.65	5.624%	$134.829	$134.83	$134.85	$134.80
7 purchase totals =	$780.80		$831.5277	$831.53	$831.55	$831.40