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 $92.96   13.239%   $105.267   $105.27   $105.25   $105.30  
  Purchase #2 $60.63   8.715%   $65.9139   $65.91   $65.90   $65.90  
  Purchase #3 $98.34   12.131%   $110.2696   $110.27   $110.25   $110.30  
  Purchase #4 $96.93   9.306%   $105.9503   $105.95   $105.95   $106.00  
  Purchase #5 $92.54   13.134%   $104.6942   $104.69   $104.70   $104.70  
  Purchase #6 $144.83   4.715%   $151.6587   $151.66   $151.65   $151.70  
  Purchase #7 $183.81   13.867%   $209.2989   $209.30   $209.30   $209.30  
  7 purchase totals = $770.04       $853.0526   $853.05   $853.00   $853.20