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 $245.63   8.592%   $266.7345   $266.73   $266.75   $266.70  
  Purchase #2 $58.63   8.379%   $63.5426   $63.54   $63.55   $63.50  
  Purchase #3 $227.37   13.291%   $257.5897   $257.59   $257.60   $257.60  
  Purchase #4 $136.91   5.190%   $144.0156   $144.02   $144.00   $144.00  
  Purchase #5 $23.87   5.504%   $25.1838   $25.18   $25.20   $25.20  
  Purchase #6 $54.78   7.689%   $58.992   $58.99   $59.00   $59.00  
  Purchase #7 $134.27   5.622%   $141.8187   $141.82   $141.80   $141.80  
  7 purchase totals = $881.46       $957.8769   $957.87   $957.90   $957.80