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	$221.80	7.386%	$238.1821	$238.18	$238.20	$238.20
Purchase #2	$42.67	9.126%	$46.5641	$46.56	$46.55	$46.60
Purchase #3	$80.48	12.488%	$90.5303	$90.53	$90.55	$90.50
Purchase #4	$110.92	5.423%	$116.9352	$116.94	$116.95	$116.90
Purchase #5	$108.89	9.797%	$119.558	$119.56	$119.55	$119.60
Purchase #6	$118.98	11.429%	$132.5782	$132.58	$132.60	$132.60
Purchase #7	$22.56	7.380%	$24.2249	$24.22	$24.20	$24.20
7 purchase totals =	$706.30		$768.5728	$768.57	$768.60	$768.60