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	$82.73	8.392%	$89.6727	$89.67	$89.65	$89.70
Purchase #2	$82.29	4.245%	$85.7832	$85.78	$85.80	$85.80
Purchase #3	$42.81	4.785%	$44.8585	$44.86	$44.85	$44.90
Purchase #4	$129.43	10.754%	$143.3489	$143.35	$143.35	$143.30
Purchase #5	$116.47	5.794%	$123.2183	$123.22	$123.20	$123.20
Purchase #6	$104.89	12.245%	$117.7338	$117.73	$117.75	$117.70
Purchase #7	$199.77	13.615%	$226.9687	$226.97	$226.95	$227.00
7 purchase totals =	$758.39		$831.5841	$831.58	$831.55	$831.60