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	$128.57	8.299%	$139.24	$139.24	$139.25	$139.20
Purchase #2	$88.28	11.684%	$98.5946	$98.59	$98.60	$98.60
Purchase #3	$79.66	13.292%	$90.2484	$90.25	$90.25	$90.20
Purchase #4	$157.92	10.457%	$174.4337	$174.43	$174.45	$174.40
Purchase #5	$166.34	10.468%	$183.7525	$183.75	$183.75	$183.80
Purchase #6	$8.52	11.236%	$9.4773	$9.48	$9.50	$9.50
Purchase #7	$209.60	13.836%	$238.6003	$238.60	$238.60	$238.60
7 purchase totals =	$838.89		$934.3468	$934.34	$934.40	$934.30