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	$137.90	11.177%	$153.3131	$153.31	$153.30	$153.30
Purchase #2	$68.60	13.854%	$78.1038	$78.10	$78.10	$78.10
Purchase #3	$9.58	13.626%	$10.8854	$10.89	$10.90	$10.90
Purchase #4	$218.25	4.374%	$227.7963	$227.80	$227.80	$227.80
Purchase #5	$153.83	12.300%	$172.7511	$172.75	$172.75	$172.80
Purchase #6	$132.39	10.352%	$146.095	$146.10	$146.10	$146.10
Purchase #7	$16.61	3.244%	$17.1488	$17.15	$17.15	$17.10
7 purchase totals =	$737.16		$806.0935	$806.10	$806.10	$806.10