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 $201.94   11.742%   $225.6518   $225.65   $225.65   $225.70  
  Purchase #2 $25.28   7.172%   $27.0931   $27.09   $27.10   $27.10  
  Purchase #3 $98.88   13.414%   $112.1438   $112.14   $112.15   $112.10  
  Purchase #4 $148.64   10.177%   $163.7671   $163.77   $163.75   $163.80  
  Purchase #5 $231.38   8.609%   $251.2995   $251.30   $251.30   $251.30  
  Purchase #6 $92.29   8.611%   $100.2371   $100.24   $100.25   $100.20  
  Purchase #7 $73.93   6.696%   $78.8804   $78.88   $78.90   $78.90  
  7 purchase totals = $872.34       $959.0728   $959.07   $959.10   $959.10