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 $67.64   13.391%   $76.6977   $76.70   $76.70   $76.70  
  Purchase #2 $211.52   5.167%   $222.4492   $222.45   $222.45   $222.40  
  Purchase #3 $29.53   10.849%   $32.7337   $32.73   $32.75   $32.70  
  Purchase #4 $5.95   10.177%   $6.5555   $6.56   $6.55   $6.60  
  Purchase #5 $164.71   6.446%   $175.3272   $175.33   $175.35   $175.30  
  Purchase #6 $198.32   12.402%   $222.9156   $222.92   $222.90   $222.90  
  Purchase #7 $187.26   7.681%   $201.6434   $201.64   $201.65   $201.60  
  7 purchase totals = $864.93       $938.3223   $938.33   $938.35   $938.20