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	$80.77	12.565%	$90.9188	$90.92	$90.90	$90.90
Purchase #2	$69.96	7.401%	$75.1377	$75.14	$75.15	$75.10
Purchase #3	$5.37	4.519%	$5.6127	$5.61	$5.60	$5.60
Purchase #4	$45.51	13.353%	$51.587	$51.59	$51.60	$51.60
Purchase #5	$100.92	6.564%	$107.5444	$107.54	$107.55	$107.50
Purchase #6	$88.98	3.540%	$92.1299	$92.13	$92.15	$92.10
Purchase #7	$192.38	3.684%	$199.4673	$199.47	$199.45	$199.50
7 purchase totals =	$583.89		$622.3978	$622.40	$622.40	$622.30