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	$38.58	10.628%	$42.6803	$42.68	$42.70	$42.70
Purchase #2	$40.69	3.443%	$42.091	$42.09	$42.10	$42.10
Purchase #3	$213.35	3.528%	$220.877	$220.88	$220.90	$220.90
Purchase #4	$21.87	13.420%	$24.805	$24.81	$24.80	$24.80
Purchase #5	$177.65	9.817%	$195.0899	$195.09	$195.10	$195.10
Purchase #6	$83.77	7.265%	$89.8559	$89.86	$89.85	$89.90
Purchase #7	$177.77	11.650%	$198.4802	$198.48	$198.50	$198.50
7 purchase totals =	$753.68		$813.8793	$813.89	$813.95	$814.00