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 $56.83   9.365%   $62.1521   $62.15   $62.15   $62.20  
  Purchase #2 $229.76   12.134%   $257.6391   $257.64   $257.65   $257.60  
  Purchase #3 $14.63   6.845%   $15.6314   $15.63   $15.65   $15.60  
  Purchase #4 $214.70   7.270%   $230.3087   $230.31   $230.30   $230.30  
  Purchase #5 $207.83   3.320%   $214.73   $214.73   $214.75   $214.70  
  Purchase #6 $28.92   12.496%   $32.5338   $32.53   $32.55   $32.50  
  Purchase #7 $130.31   8.816%   $141.7981   $141.80   $141.80   $141.80  
  7 purchase totals = $882.98       $954.7932   $954.79   $954.85   $954.70