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	$136.87	4.729%	$143.3426	$143.34	$143.35	$143.30
Purchase #2	$34.81	11.241%	$38.723	$38.72	$38.70	$38.70
Purchase #3	$35.67	4.127%	$37.1421	$37.14	$37.15	$37.10
Purchase #4	$18.60	13.666%	$21.1419	$21.14	$21.15	$21.10
Purchase #5	$26.94	7.522%	$28.9664	$28.97	$28.95	$29.00
Purchase #6	$14.44	3.339%	$14.9222	$14.92	$14.90	$14.90
Purchase #7	$152.45	7.659%	$164.1261	$164.13	$164.15	$164.10
7 purchase totals =	$419.78		$448.3643	$448.36	$448.35	$448.20