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	$102.49	12.533%	$115.3351	$115.34	$115.35	$115.30
Purchase #2	$105.47	10.661%	$116.7142	$116.71	$116.70	$116.70
Purchase #3	$133.57	4.735%	$139.8945	$139.89	$139.90	$139.90
Purchase #4	$72.89	5.568%	$76.9485	$76.95	$76.95	$76.90
Purchase #5	$238.57	6.103%	$253.1299	$253.13	$253.15	$253.10
Purchase #6	$159.76	3.659%	$165.6056	$165.61	$165.60	$165.60
Purchase #7	$178.25	6.613%	$190.0377	$190.04	$190.05	$190.00
7 purchase totals =	$991.00		$1,057.6655	$1,057.67	$1,057.70	$1,057.50