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	$109.88	12.386%	$123.4897	$123.49	$123.50	$123.50
Purchase #2	$100.57	12.105%	$112.744	$112.74	$112.75	$112.70
Purchase #3	$94.82	12.789%	$106.9465	$106.95	$106.95	$106.90
Purchase #4	$72.64	8.664%	$78.9335	$78.93	$78.95	$78.90
Purchase #5	$209.84	13.584%	$238.3447	$238.34	$238.35	$238.30
Purchase #6	$23.70	5.536%	$25.012	$25.01	$25.00	$25.00
Purchase #7	$196.96	9.305%	$215.2871	$215.29	$215.30	$215.30
7 purchase totals =	$808.41		$900.7575	$900.75	$900.80	$900.60