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	$79.43	12.287%	$89.1896	$89.19	$89.20	$89.20
Purchase #2	$134.32	3.572%	$139.1179	$139.12	$139.10	$139.10
Purchase #3	$133.62	7.644%	$143.8339	$143.83	$143.85	$143.80
Purchase #4	$80.44	8.574%	$87.3369	$87.34	$87.35	$87.30
Purchase #5	$37.97	10.868%	$42.0966	$42.10	$42.10	$42.10
Purchase #6	$24.34	3.732%	$25.2484	$25.25	$25.25	$25.20
Purchase #7	$207.78	10.444%	$229.4805	$229.48	$229.50	$229.50
7 purchase totals =	$697.90		$756.3038	$756.31	$756.35	$756.20