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	$69.73	5.441%	$73.524	$73.52	$73.50	$73.50
Purchase #2	$141.28	8.221%	$152.8946	$152.89	$152.90	$152.90
Purchase #3	$129.58	12.329%	$145.5559	$145.56	$145.55	$145.60
Purchase #4	$80.34	8.167%	$86.9014	$86.90	$86.90	$86.90
Purchase #5	$19.67	6.763%	$21.0003	$21.00	$21.00	$21.00
Purchase #6	$116.87	5.491%	$123.2873	$123.29	$123.30	$123.30
Purchase #7	$242.94	5.526%	$256.3649	$256.36	$256.35	$256.40
7 purchase totals =	$800.41		$859.5284	$859.52	$859.50	$859.60