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	$137.69	6.226%	$146.2626	$146.26	$146.25	$146.30
Purchase #2	$247.29	9.691%	$271.2549	$271.25	$271.25	$271.30
Purchase #3	$104.54	3.857%	$108.5721	$108.57	$108.55	$108.60
Purchase #4	$32.43	6.411%	$34.5091	$34.51	$34.50	$34.50
Purchase #5	$61.48	7.262%	$65.9447	$65.94	$65.95	$65.90
Purchase #6	$218.38	4.327%	$227.8293	$227.83	$227.85	$227.80
Purchase #7	$194.51	8.300%	$210.6543	$210.65	$210.65	$210.70
7 purchase totals =	$996.32		$1,065.0270	$1,065.01	$1,065.00	$1,065.10