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	$153.33	11.248%	$170.5766	$170.58	$170.60	$170.60
Purchase #2	$200.88	13.238%	$227.4725	$227.47	$227.45	$227.50
Purchase #3	$146.78	13.682%	$166.8624	$166.86	$166.85	$166.90
Purchase #4	$127.50	4.365%	$133.0654	$133.07	$133.05	$133.10
Purchase #5	$210.45	10.626%	$232.8124	$232.81	$232.80	$232.80
Purchase #6	$145.82	11.288%	$162.2802	$162.28	$162.30	$162.30
Purchase #7	$35.44	6.605%	$37.7808	$37.78	$37.80	$37.80
7 purchase totals =	$1,020.20		$1,130.8503	$1,130.85	$1,130.85	$1,131.00