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	$81.93	10.536%	$90.5621	$90.56	$90.55	$90.60
Purchase #2	$81.48	7.856%	$87.8811	$87.88	$87.90	$87.90
Purchase #3	$30.78	6.301%	$32.7194	$32.72	$32.70	$32.70
Purchase #4	$239.91	4.508%	$250.7251	$250.73	$250.75	$250.70
Purchase #5	$28.35	11.619%	$31.644	$31.64	$31.65	$31.60
Purchase #6	$75.57	5.702%	$79.879	$79.88	$79.90	$79.90
Purchase #7	$158.51	6.471%	$168.7672	$168.77	$168.75	$168.80
7 purchase totals =	$696.53		$742.1779	$742.18	$742.20	$742.20