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	$32.98	7.181%	$35.3483	$35.35	$35.35	$35.30
Purchase #2	$173.58	9.784%	$190.5631	$190.56	$190.55	$190.60
Purchase #3	$147.39	9.837%	$161.8888	$161.89	$161.90	$161.90
Purchase #4	$235.85	4.559%	$246.6024	$246.60	$246.60	$246.60
Purchase #5	$164.32	13.141%	$185.9133	$185.91	$185.90	$185.90
Purchase #6	$52.31	4.486%	$54.6566	$54.66	$54.65	$54.70
Purchase #7	$66.94	7.277%	$71.8112	$71.81	$71.80	$71.80
7 purchase totals =	$873.37		$946.7837	$946.78	$946.75	$946.80