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	$73.32	11.274%	$81.5861	$81.59	$81.60	$81.60
Purchase #2	$71.96	13.862%	$81.9351	$81.94	$81.95	$81.90
Purchase #3	$17.68	6.679%	$18.8608	$18.86	$18.85	$18.90
Purchase #4	$104.94	8.502%	$113.862	$113.86	$113.85	$113.90
Purchase #5	$124.62	10.561%	$137.7811	$137.78	$137.80	$137.80
Purchase #6	$37.88	12.275%	$42.5298	$42.53	$42.55	$42.50
Purchase #7	$33.58	4.802%	$35.1925	$35.19	$35.20	$35.20
7 purchase totals =	$463.98		$511.7474	$511.75	$511.80	$511.80