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	$144.89	11.413%	$161.4263	$161.43	$161.45	$161.40
Purchase #2	$51.34	8.315%	$55.6089	$55.61	$55.60	$55.60
Purchase #3	$38.35	5.516%	$40.4654	$40.47	$40.45	$40.50
Purchase #4	$161.47	7.818%	$174.0937	$174.09	$174.10	$174.10
Purchase #5	$202.89	8.366%	$219.8638	$219.86	$219.85	$219.90
Purchase #6	$162.50	11.169%	$180.6496	$180.65	$180.65	$180.60
Purchase #7	$131.79	5.838%	$139.4839	$139.48	$139.50	$139.50
7 purchase totals =	$893.23		$971.5916	$971.59	$971.60	$971.60