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 $105.83   7.496%   $113.763   $113.76   $113.75   $113.80  
  Purchase #2 $166.69   13.605%   $189.3682   $189.37   $189.35   $189.40  
  Purchase #3 $102.38   7.677%   $110.2397   $110.24   $110.25   $110.20  
  Purchase #4 $107.62   13.388%   $122.0282   $122.03   $122.05   $122.00  
  Purchase #5 $105.47   13.441%   $119.6462   $119.65   $119.65   $119.60  
  Purchase #6 $109.95   13.137%   $124.3941   $124.39   $124.40   $124.40  
  Purchase #7 $45.36   4.850%   $47.56   $47.56   $47.55   $47.60  
  7 purchase totals = $743.30       $826.9994   $827.00   $827.00   $827.00