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	$139.47	8.144%	$150.8284	$150.83	$150.85	$150.80
Purchase #2	$12.57	5.411%	$13.2502	$13.25	$13.25	$13.30
Purchase #3	$146.84	3.283%	$151.6608	$151.66	$151.65	$151.70
Purchase #4	$189.68	3.840%	$196.9637	$196.96	$196.95	$197.00
Purchase #5	$209.44	6.426%	$222.8986	$222.90	$222.90	$222.90
Purchase #6	$84.57	11.853%	$94.5941	$94.59	$94.60	$94.60
Purchase #7	$35.51	12.648%	$40.0013	$40.00	$40.00	$40.00
7 purchase totals =	$818.08		$870.1971	$870.19	$870.20	$870.30