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 $226.98   13.533%   $257.6972   $257.70   $257.70   $257.70  
  Purchase #2 $237.99   4.565%   $248.8542   $248.85   $248.85   $248.90  
  Purchase #3 $6.37   3.687%   $6.6049   $6.60   $6.60   $6.60  
  Purchase #4 $224.73   12.786%   $253.464   $253.46   $253.45   $253.50  
  Purchase #5 $64.31   9.531%   $70.4394   $70.44   $70.45   $70.40  
  Purchase #6 $219.88   7.382%   $236.1115   $236.11   $236.10   $236.10  
  Purchase #7 $165.56   13.334%   $187.6358   $187.64   $187.65   $187.60  
  7 purchase totals = $1,145.82       $1,260.8070   $1,260.80   $1,260.80   $1,260.80