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	$241.57	13.225%	$273.5176	$273.52	$273.50	$273.50
Purchase #2	$38.35	9.164%	$41.8644	$41.86	$41.85	$41.90
Purchase #3	$249.62	13.590%	$283.5434	$283.54	$283.55	$283.50
Purchase #4	$97.93	10.759%	$108.4663	$108.47	$108.45	$108.50
Purchase #5	$44.51	13.557%	$50.5442	$50.54	$50.55	$50.50
Purchase #6	$31.66	5.434%	$33.3804	$33.38	$33.40	$33.40
Purchase #7	$23.32	9.446%	$25.5228	$25.52	$25.50	$25.50
7 purchase totals =	$726.96		$816.8391	$816.83	$816.80	$816.80