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	$153.64	8.561%	$166.7931	$166.79	$166.80	$166.80
Purchase #2	$104.85	11.143%	$116.5334	$116.53	$116.55	$116.50
Purchase #3	$196.67	11.693%	$219.6666	$219.67	$219.65	$219.70
Purchase #4	$39.89	9.319%	$43.6073	$43.61	$43.60	$43.60
Purchase #5	$141.37	9.182%	$154.3506	$154.35	$154.35	$154.40
Purchase #6	$6.35	10.400%	$7.0104	$7.01	$7.00	$7.00
Purchase #7	$223.46	3.768%	$231.88	$231.88	$231.90	$231.90
7 purchase totals =	$866.23		$939.8414	$939.84	$939.85	$939.90