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	$158.89	6.249%	$168.819	$168.82	$168.80	$168.80
Purchase #2	$141.89	12.649%	$159.8377	$159.84	$159.85	$159.80
Purchase #3	$122.77	10.641%	$135.834	$135.83	$135.85	$135.80
Purchase #4	$140.37	7.290%	$150.603	$150.60	$150.60	$150.60
Purchase #5	$6.82	11.175%	$7.5821	$7.58	$7.60	$7.60
Purchase #6	$26.65	9.567%	$29.1996	$29.20	$29.20	$29.20
Purchase #7	$103.41	7.404%	$111.0665	$111.07	$111.05	$111.10
7 purchase totals =	$700.80		$762.9419	$762.94	$762.95	$762.90