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	$102.29	9.862%	$112.3778	$112.38	$112.40	$112.40
Purchase #2	$16.58	5.762%	$17.5353	$17.54	$17.55	$17.50
Purchase #3	$23.57	3.827%	$24.472	$24.47	$24.45	$24.50
Purchase #4	$83.39	10.522%	$92.1643	$92.16	$92.15	$92.20
Purchase #5	$88.31	3.584%	$91.475	$91.48	$91.50	$91.50
Purchase #6	$106.86	9.287%	$116.7841	$116.78	$116.80	$116.80
Purchase #7	$78.67	9.534%	$86.1704	$86.17	$86.15	$86.20
7 purchase totals =	$499.67		$540.9789	$540.98	$541.00	$541.10