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 $223.95   6.600%   $238.7307   $238.73   $238.75   $238.70  
  Purchase #2 $27.46   12.692%   $30.9452   $30.95   $30.95   $30.90  
  Purchase #3 $53.49   5.499%   $56.4314   $56.43   $56.45   $56.40  
  Purchase #4 $152.92   13.582%   $173.6896   $173.69   $173.70   $173.70  
  Purchase #5 $212.58   11.619%   $237.2797   $237.28   $237.30   $237.30  
  Purchase #6 $45.29   3.687%   $46.9598   $46.96   $46.95   $47.00  
  Purchase #7 $162.38   5.832%   $171.85   $171.85   $171.85   $171.90  
  7 purchase totals = $878.07       $955.8864   $955.89   $955.95   $955.90