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	$243.80	9.257%	$266.3686	$266.37	$266.35	$266.40
Purchase #2	$123.96	11.617%	$138.3604	$138.36	$138.35	$138.40
Purchase #3	$102.79	8.649%	$111.6803	$111.68	$111.70	$111.70
Purchase #4	$166.59	3.303%	$172.0925	$172.09	$172.10	$172.10
Purchase #5	$37.73	6.475%	$40.173	$40.17	$40.15	$40.20
Purchase #6	$12.31	9.434%	$13.4713	$13.47	$13.45	$13.50
Purchase #7	$111.33	12.405%	$125.1405	$125.14	$125.15	$125.10
7 purchase totals =	$798.51		$867.2866	$867.28	$867.25	$867.40