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	$45.91	10.853%	$50.8926	$50.89	$50.90	$50.90
Purchase #2	$92.93	7.706%	$100.0912	$100.09	$100.10	$100.10
Purchase #3	$213.58	6.270%	$226.9715	$226.97	$226.95	$227.00
Purchase #4	$205.73	6.811%	$219.7423	$219.74	$219.75	$219.70
Purchase #5	$79.48	7.863%	$85.7295	$85.73	$85.75	$85.70
Purchase #6	$213.76	11.617%	$238.5925	$238.59	$238.60	$238.60
Purchase #7	$87.75	3.189%	$90.5483	$90.55	$90.55	$90.50
7 purchase totals =	$939.14		$1,012.5679	$1,012.56	$1,012.60	$1,012.50