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	$39.52	6.703%	$42.169	$42.17	$42.15	$42.20
Purchase #2	$187.73	8.626%	$203.9236	$203.92	$203.90	$203.90
Purchase #3	$142.44	9.840%	$156.4561	$156.46	$156.45	$156.50
Purchase #4	$142.72	8.772%	$155.2394	$155.24	$155.25	$155.20
Purchase #5	$104.83	7.193%	$112.3704	$112.37	$112.35	$112.40
Purchase #6	$227.67	4.790%	$238.5754	$238.58	$238.60	$238.60
Purchase #7	$156.62	5.105%	$164.6155	$164.62	$164.60	$164.60
7 purchase totals =	$1,001.53		$1,073.3494	$1,073.36	$1,073.30	$1,073.40