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 $236.26   13.506%   $268.1693   $268.17   $268.15   $268.20  
  Purchase #2 $116.48   5.316%   $122.6721   $122.67   $122.65   $122.70  
  Purchase #3 $218.78   4.387%   $228.3779   $228.38   $228.40   $228.40  
  Purchase #4 $74.98   6.283%   $79.691   $79.69   $79.70   $79.70  
  Purchase #5 $90.40   4.756%   $94.6994   $94.70   $94.70   $94.70  
  Purchase #6 $168.62   6.631%   $179.8012   $179.80   $179.80   $179.80  
  Purchase #7 $134.38   13.492%   $152.5105   $152.51   $152.50   $152.50  
  7 purchase totals = $1,039.90       $1,125.9214   $1,125.92   $1,125.90   $1,126.00