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 $227.71   13.255%   $257.893   $257.89   $257.90   $257.90  
  Purchase #2 $111.58   6.497%   $118.8294   $118.83   $118.85   $118.80  
  Purchase #3 $58.74   6.211%   $62.3883   $62.39   $62.40   $62.40  
  Purchase #4 $80.78   3.137%   $83.3141   $83.31   $83.30   $83.30  
  Purchase #5 $220.34   5.354%   $232.137   $232.14   $232.15   $232.10  
  Purchase #6 $139.25   5.235%   $146.5397   $146.54   $146.55   $146.50  
  Purchase #7 $236.29   6.569%   $251.8119   $251.81   $251.80   $251.80  
  7 purchase totals = $1,074.69       $1,152.9134   $1,152.91   $1,152.95   $1,152.80