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	$18.46	7.667%	$19.8753	$19.88	$19.90	$19.90
Purchase #2	$164.35	4.455%	$171.6718	$171.67	$171.65	$171.70
Purchase #3	$22.99	8.302%	$24.8986	$24.90	$24.90	$24.90
Purchase #4	$177.35	7.600%	$190.8286	$190.83	$190.85	$190.80
Purchase #5	$229.51	7.139%	$245.8947	$245.89	$245.90	$245.90
Purchase #6	$45.90	13.777%	$52.2236	$52.22	$52.20	$52.20
Purchase #7	$104.68	4.548%	$109.4408	$109.44	$109.45	$109.40
7 purchase totals =	$763.24		$814.8334	$814.83	$814.85	$814.80