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	$91.90	8.535%	$99.7437	$99.74	$99.75	$99.70
Purchase #2	$117.30	13.242%	$132.8329	$132.83	$132.85	$132.80
Purchase #3	$208.72	4.199%	$217.4842	$217.48	$217.50	$217.50
Purchase #4	$77.84	10.233%	$85.8054	$85.81	$85.80	$85.80
Purchase #5	$219.48	7.303%	$235.5086	$235.51	$235.50	$235.50
Purchase #6	$161.27	9.707%	$176.9245	$176.92	$176.90	$176.90
Purchase #7	$40.51	5.790%	$42.8555	$42.86	$42.85	$42.90
7 purchase totals =	$917.02		$991.1548	$991.15	$991.15	$991.10