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	$128.77	5.779%	$136.2116	$136.21	$136.20	$136.20
Purchase #2	$138.81	3.134%	$143.1603	$143.16	$143.15	$143.20
Purchase #3	$140.72	12.872%	$158.8335	$158.83	$158.85	$158.80
Purchase #4	$139.76	7.800%	$150.6613	$150.66	$150.65	$150.70
Purchase #5	$107.76	3.582%	$111.62	$111.62	$111.60	$111.60
Purchase #6	$141.41	3.814%	$146.8034	$146.80	$146.80	$146.80
Purchase #7	$118.38	12.126%	$132.7348	$132.73	$132.75	$132.70
7 purchase totals =	$915.61		$980.0249	$980.01	$980.00	$980.00