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	$11.92	10.746%	$13.2009	$13.20	$13.20	$13.20
Purchase #2	$42.87	7.670%	$46.1581	$46.16	$46.15	$46.20
Purchase #3	$134.74	4.282%	$140.5096	$140.51	$140.50	$140.50
Purchase #4	$69.73	12.733%	$78.6087	$78.61	$78.60	$78.60
Purchase #5	$52.60	4.193%	$54.8055	$54.81	$54.80	$54.80
Purchase #6	$90.96	8.342%	$98.5479	$98.55	$98.55	$98.50
Purchase #7	$161.88	4.115%	$168.5414	$168.54	$168.55	$168.50
7 purchase totals =	$564.70		$600.3721	$600.38	$600.35	$600.30