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 $216.96   6.641%   $231.3683   $231.37   $231.35   $231.40  
  Purchase #2 $21.53   9.544%   $23.5848   $23.58   $23.60   $23.60  
  Purchase #3 $89.36   8.777%   $97.2031   $97.20   $97.20   $97.20  
  Purchase #4 $230.68   10.451%   $254.7884   $254.79   $254.80   $254.80  
  Purchase #5 $247.59   5.730%   $261.7769   $261.78   $261.80   $261.80  
  Purchase #6 $238.39   3.308%   $246.2759   $246.28   $246.30   $246.30  
  Purchase #7 $215.63   12.572%   $242.739   $242.74   $242.75   $242.70  
  7 purchase totals = $1,260.14       $1,357.7364   $1,357.74   $1,357.80   $1,357.80