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	$32.57	3.706%	$33.777	$33.78	$33.80	$33.80
Purchase #2	$40.52	7.221%	$43.4459	$43.45	$43.45	$43.40
Purchase #3	$21.71	12.835%	$24.4965	$24.50	$24.50	$24.50
Purchase #4	$201.53	8.688%	$219.0389	$219.04	$219.05	$219.00
Purchase #5	$186.71	12.511%	$210.0693	$210.07	$210.05	$210.10
Purchase #6	$18.68	13.595%	$21.2195	$21.22	$21.20	$21.20
Purchase #7	$114.66	7.788%	$123.5897	$123.59	$123.60	$123.60
7 purchase totals =	$616.38		$675.6368	$675.65	$675.65	$675.60