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 $78.71   5.129%   $82.747   $82.75   $82.75   $82.70  
  Purchase #2 $23.48   12.610%   $26.4408   $26.44   $26.45   $26.40  
  Purchase #3 $177.81   5.644%   $187.8456   $187.85   $187.85   $187.80  
  Purchase #4 $234.38   13.634%   $266.3354   $266.34   $266.35   $266.30  
  Purchase #5 $123.59   9.775%   $135.6709   $135.67   $135.65   $135.70  
  Purchase #6 $41.54   10.331%   $45.8315   $45.83   $45.85   $45.80  
  Purchase #7 $182.51   8.358%   $197.7642   $197.76   $197.75   $197.80  
  7 purchase totals = $862.02       $942.6354   $942.64   $942.65   $942.50