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	$37.56	5.178%	$39.5049	$39.50	$39.50	$39.50
Purchase #2	$172.31	11.625%	$192.341	$192.34	$192.35	$192.30
Purchase #3	$24.85	3.105%	$25.6216	$25.62	$25.60	$25.60
Purchase #4	$171.93	4.848%	$180.2652	$180.27	$180.25	$180.30
Purchase #5	$93.26	12.136%	$104.578	$104.58	$104.60	$104.60
Purchase #6	$132.61	8.747%	$144.2094	$144.21	$144.20	$144.20
Purchase #7	$54.31	12.139%	$60.9027	$60.90	$60.90	$60.90
7 purchase totals =	$686.83		$747.4228	$747.42	$747.40	$747.40