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	$138.58	3.224%	$143.0478	$143.05	$143.05	$143.00
Purchase #2	$82.79	3.355%	$85.5676	$85.57	$85.55	$85.60
Purchase #3	$193.31	8.567%	$209.8709	$209.87	$209.85	$209.90
Purchase #4	$168.38	11.255%	$187.3312	$187.33	$187.35	$187.30
Purchase #5	$28.41	3.507%	$29.4063	$29.41	$29.40	$29.40
Purchase #6	$238.89	11.530%	$266.434	$266.43	$266.45	$266.40
Purchase #7	$20.25	7.660%	$21.8012	$21.80	$21.80	$21.80
7 purchase totals =	$870.61		$943.4590	$943.46	$943.45	$943.40