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	$30.74	12.204%	$34.4915	$34.49	$34.50	$34.50
Purchase #2	$212.85	4.846%	$223.1647	$223.16	$223.15	$223.20
Purchase #3	$213.48	11.189%	$237.3663	$237.37	$237.35	$237.40
Purchase #4	$69.76	12.553%	$78.517	$78.52	$78.50	$78.50
Purchase #5	$113.43	12.135%	$127.1947	$127.19	$127.20	$127.20
Purchase #6	$66.36	10.741%	$73.4877	$73.49	$73.50	$73.50
Purchase #7	$132.31	5.637%	$139.7683	$139.77	$139.75	$139.80
7 purchase totals =	$838.93		$913.9902	$913.99	$913.95	$914.10