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	$101.64	12.650%	$114.4975	$114.50	$114.50	$114.50
Purchase #2	$79.85	4.711%	$83.6117	$83.61	$83.60	$83.60
Purchase #3	$103.78	12.288%	$116.5325	$116.53	$116.55	$116.50
Purchase #4	$93.70	8.807%	$101.9522	$101.95	$101.95	$102.00
Purchase #5	$53.67	12.766%	$60.5215	$60.52	$60.50	$60.50
Purchase #6	$222.57	5.561%	$234.9471	$234.95	$234.95	$234.90
Purchase #7	$139.69	13.687%	$158.8094	$158.81	$158.80	$158.80
7 purchase totals =	$794.90		$870.8719	$870.87	$870.85	$870.80