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 $9.31   6.616%   $9.9259   $9.93   $9.95   $9.90  
  Purchase #2 $93.34   13.291%   $105.7458   $105.75   $105.75   $105.70  
  Purchase #3 $225.44   7.747%   $242.9048   $242.90   $242.90   $242.90  
  Purchase #4 $105.80   12.118%   $118.6208   $118.62   $118.60   $118.60  
  Purchase #5 $189.77   4.354%   $198.0326   $198.03   $198.05   $198.00  
  Purchase #6 $17.68   7.492%   $19.0046   $19.00   $19.00   $19.00  
  Purchase #7 $25.82   4.382%   $26.9514   $26.95   $26.95   $27.00  
  7 purchase totals = $667.16       $721.1859   $721.18   $721.20   $721.10