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 $167.25   8.464%   $181.406   $181.41   $181.40   $181.40  
  Purchase #2 $89.81   4.548%   $93.8946   $93.89   $93.90   $93.90  
  Purchase #3 $138.63   7.666%   $149.2574   $149.26   $149.25   $149.30  
  Purchase #4 $154.31   7.329%   $165.6194   $165.62   $165.60   $165.60  
  Purchase #5 $234.37   11.766%   $261.946   $261.95   $261.95   $261.90  
  Purchase #6 $66.59   5.771%   $70.4329   $70.43   $70.45   $70.40  
  Purchase #7 $122.93   11.147%   $136.633   $136.63   $136.65   $136.60  
  7 purchase totals = $973.89       $1,059.1893   $1,059.19   $1,059.20   $1,059.10