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 $176.92   13.642%   $201.0554   $201.06   $201.05   $201.10  
  Purchase #2 $71.89   12.537%   $80.9028   $80.90   $80.90   $80.90  
  Purchase #3 $224.89   13.709%   $255.7202   $255.72   $255.70   $255.70  
  Purchase #4 $53.57   10.141%   $59.0025   $59.00   $59.00   $59.00  
  Purchase #5 $113.70   6.592%   $121.1951   $121.20   $121.20   $121.20  
  Purchase #6 $45.46   8.587%   $49.3637   $49.36   $49.35   $49.40  
  Purchase #7 $195.80   3.139%   $201.9462   $201.95   $201.95   $201.90  
  7 purchase totals = $882.23       $969.1859   $969.19   $969.15   $969.20