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	$137.71	10.531%	$152.2122	$152.21	$152.20	$152.20
Purchase #2	$18.96	7.365%	$20.3564	$20.36	$20.35	$20.40
Purchase #3	$177.98	10.487%	$196.6448	$196.64	$196.65	$196.60
Purchase #4	$217.75	4.480%	$227.5052	$227.51	$227.50	$227.50
Purchase #5	$109.46	7.646%	$117.8293	$117.83	$117.85	$117.80
Purchase #6	$96.47	3.863%	$100.1966	$100.20	$100.20	$100.20
Purchase #7	$31.67	10.729%	$35.0679	$35.07	$35.05	$35.10
7 purchase totals =	$790.00		$849.8124	$849.82	$849.80	$849.80