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	$35.54	8.420%	$38.5325	$38.53	$38.55	$38.50
Purchase #2	$231.38	11.845%	$258.787	$258.79	$258.80	$258.80
Purchase #3	$74.71	10.520%	$82.5695	$82.57	$82.55	$82.60
Purchase #4	$127.55	6.853%	$136.291	$136.29	$136.30	$136.30
Purchase #5	$153.94	7.847%	$166.0197	$166.02	$166.00	$166.00
Purchase #6	$210.48	10.175%	$231.8963	$231.90	$231.90	$231.90
Purchase #7	$76.75	11.208%	$85.3521	$85.35	$85.35	$85.40
7 purchase totals =	$910.35		$999.4481	$999.45	$999.45	$999.50