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	$113.61	8.733%	$123.5316	$123.53	$123.55	$123.50
Purchase #2	$232.81	3.342%	$240.5905	$240.59	$240.60	$240.60
Purchase #3	$90.32	13.161%	$102.207	$102.21	$102.20	$102.20
Purchase #4	$101.51	4.116%	$105.6882	$105.69	$105.70	$105.70
Purchase #5	$34.86	13.620%	$39.6079	$39.61	$39.60	$39.60
Purchase #6	$56.35	4.640%	$58.9646	$58.96	$58.95	$59.00
Purchase #7	$139.62	8.533%	$151.5338	$151.53	$151.55	$151.50
7 purchase totals =	$769.08		$822.1236	$822.12	$822.15	$822.10