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	$37.43	8.620%	$40.6565	$40.66	$40.65	$40.70
Purchase #2	$82.58	6.410%	$87.8734	$87.87	$87.85	$87.90
Purchase #3	$121.64	10.776%	$134.7479	$134.75	$134.75	$134.70
Purchase #4	$86.48	4.508%	$90.3785	$90.38	$90.40	$90.40
Purchase #5	$76.75	5.209%	$80.7479	$80.75	$80.75	$80.70
Purchase #6	$130.53	9.669%	$143.1509	$143.15	$143.15	$143.20
Purchase #7	$35.29	5.338%	$37.1738	$37.17	$37.15	$37.20
7 purchase totals =	$570.70		$614.7289	$614.73	$614.70	$614.80