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 $88.70   7.291%   $95.1671   $95.17   $95.15   $95.20  
  Purchase #2 $226.90   13.581%   $257.7153   $257.72   $257.70   $257.70  
  Purchase #3 $23.95   6.766%   $25.5705   $25.57   $25.55   $25.60  
  Purchase #4 $182.69   7.725%   $196.8028   $196.80   $196.80   $196.80  
  Purchase #5 $203.63   12.203%   $228.479   $228.48   $228.50   $228.50  
  Purchase #6 $86.39   8.766%   $93.9629   $93.96   $93.95   $94.00  
  Purchase #7 $215.33   12.228%   $241.6606   $241.66   $241.65   $241.70  
  7 purchase totals = $1,027.59       $1,139.3582   $1,139.36   $1,139.30   $1,139.50