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 $69.55   8.501%   $75.4624   $75.46   $75.45   $75.50  
  Purchase #2 $174.63   6.759%   $186.4332   $186.43   $186.45   $186.40  
  Purchase #3 $103.93   12.709%   $117.1385   $117.14   $117.15   $117.10  
  Purchase #4 $98.70   3.769%   $102.42   $102.42   $102.40   $102.40  
  Purchase #5 $143.43   8.557%   $155.7033   $155.70   $155.70   $155.70  
  Purchase #6 $60.54   12.702%   $68.2298   $68.23   $68.25   $68.20  
  Purchase #7 $230.48   12.275%   $258.7714   $258.77   $258.75   $258.80  
  7 purchase totals = $881.26       $964.1586   $964.15   $964.15   $964.10