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	$213.66	12.310%	$239.9615	$239.96	$239.95	$240.00
Purchase #2	$162.59	5.376%	$171.3308	$171.33	$171.35	$171.30
Purchase #3	$100.80	11.626%	$112.519	$112.52	$112.50	$112.50
Purchase #4	$99.97	6.598%	$106.566	$106.57	$106.55	$106.60
Purchase #5	$54.59	6.111%	$57.926	$57.93	$57.95	$57.90
Purchase #6	$40.56	6.724%	$43.2873	$43.29	$43.30	$43.30
Purchase #7	$197.30	5.826%	$208.7947	$208.79	$208.80	$208.80
7 purchase totals =	$869.47		$940.3853	$940.39	$940.40	$940.40