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	$11.94	7.709%	$12.8605	$12.86	$12.85	$12.90
Purchase #2	$152.54	9.224%	$166.6103	$166.61	$166.60	$166.60
Purchase #3	$89.61	11.110%	$99.5657	$99.57	$99.55	$99.60
Purchase #4	$39.92	10.840%	$44.2473	$44.25	$44.25	$44.20
Purchase #5	$30.86	8.811%	$33.5791	$33.58	$33.60	$33.60
Purchase #6	$119.87	13.411%	$135.9458	$135.95	$135.95	$135.90
Purchase #7	$76.41	12.169%	$85.7083	$85.71	$85.70	$85.70
7 purchase totals =	$521.15		$578.5170	$578.53	$578.50	$578.50