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	$17.64	12.759%	$19.8907	$19.89	$19.90	$19.90
Purchase #2	$173.68	8.697%	$188.7849	$188.78	$188.80	$188.80
Purchase #3	$225.69	13.356%	$255.8332	$255.83	$255.85	$255.80
Purchase #4	$111.78	6.742%	$119.3162	$119.32	$119.30	$119.30
Purchase #5	$87.92	7.614%	$94.6142	$94.61	$94.60	$94.60
Purchase #6	$165.86	7.855%	$178.8883	$178.89	$178.90	$178.90
Purchase #7	$88.26	11.192%	$98.1381	$98.14	$98.15	$98.10
7 purchase totals =	$870.83		$955.4656	$955.46	$955.50	$955.40