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 $176.52   8.794%   $192.0432   $192.04   $192.05   $192.00  
  Purchase #2 $60.39   13.168%   $68.3422   $68.34   $68.35   $68.30  
  Purchase #3 $216.91   9.533%   $237.588   $237.59   $237.60   $237.60  
  Purchase #4 $114.34   3.531%   $118.3773   $118.38   $118.40   $118.40  
  Purchase #5 $52.26   13.163%   $59.139   $59.14   $59.15   $59.10  
  Purchase #6 $30.38   12.601%   $34.2082   $34.21   $34.20   $34.20  
  Purchase #7 $191.96   7.456%   $206.2725   $206.27   $206.25   $206.30  
  7 purchase totals = $842.76       $915.9704   $915.97   $916.00   $915.90