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 $236.86   12.826%   $267.2397   $267.24   $267.25   $267.20  
  Purchase #2 $197.60   3.264%   $204.0497   $204.05   $204.05   $204.00  
  Purchase #3 $52.39   5.848%   $55.4538   $55.45   $55.45   $55.50  
  Purchase #4 $248.54   13.336%   $281.6853   $281.69   $281.70   $281.70  
  Purchase #5 $216.89   4.141%   $225.8714   $225.87   $225.85   $225.90  
  Purchase #6 $41.26   9.382%   $45.131   $45.13   $45.15   $45.10  
  Purchase #7 $249.90   3.722%   $259.2013   $259.20   $259.20   $259.20  
  7 purchase totals = $1,243.44       $1,338.6322   $1,338.63   $1,338.65   $1,338.60