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	$10.28	4.355%	$10.7277	$10.73	$10.75	$10.70
Purchase #2	$187.94	13.681%	$213.6521	$213.65	$213.65	$213.70
Purchase #3	$131.51	5.795%	$139.131	$139.13	$139.15	$139.10
Purchase #4	$78.40	8.771%	$85.2765	$85.28	$85.30	$85.30
Purchase #5	$143.46	9.403%	$156.9495	$156.95	$156.95	$156.90
Purchase #6	$121.87	8.193%	$131.8548	$131.85	$131.85	$131.90
Purchase #7	$78.81	12.200%	$88.4248	$88.42	$88.40	$88.40
7 purchase totals =	$752.27		$826.0164	$826.01	$826.05	$826.00