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	$124.85	5.863%	$132.17	$132.17	$132.15	$132.20
Purchase #2	$143.69	5.457%	$151.5312	$151.53	$151.55	$151.50
Purchase #3	$108.66	13.323%	$123.1368	$123.14	$123.15	$123.10
Purchase #4	$53.93	4.731%	$56.4814	$56.48	$56.50	$56.50
Purchase #5	$45.97	12.771%	$51.8408	$51.84	$51.85	$51.80
Purchase #6	$203.55	9.384%	$222.6511	$222.65	$222.65	$222.70
Purchase #7	$232.52	4.358%	$242.6532	$242.65	$242.65	$242.70
7 purchase totals =	$913.17		$980.4645	$980.46	$980.50	$980.50