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	$247.90	9.733%	$272.0281	$272.03	$272.05	$272.00
Purchase #2	$158.76	11.324%	$176.738	$176.74	$176.75	$176.70
Purchase #3	$11.75	4.126%	$12.2348	$12.23	$12.25	$12.20
Purchase #4	$94.29	5.234%	$99.2251	$99.23	$99.25	$99.20
Purchase #5	$145.90	11.574%	$162.7865	$162.79	$162.80	$162.80
Purchase #6	$49.59	6.667%	$52.8962	$52.90	$52.90	$52.90
Purchase #7	$77.34	10.466%	$85.4344	$85.43	$85.45	$85.40
7 purchase totals =	$785.53		$861.3431	$861.35	$861.45	$861.20