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 $58.88   13.831%   $67.0237   $67.02   $67.00   $67.00  
  Purchase #2 $17.37   9.498%   $19.0198   $19.02   $19.00   $19.00  
  Purchase #3 $247.60   7.457%   $266.0635   $266.06   $266.05   $266.10  
  Purchase #4 $211.66   4.524%   $221.2355   $221.24   $221.25   $221.20  
  Purchase #5 $59.42   3.767%   $61.6584   $61.66   $61.65   $61.70  
  Purchase #6 $24.69   5.112%   $25.9522   $25.95   $25.95   $26.00  
  Purchase #7 $51.38   8.740%   $55.8706   $55.87   $55.85   $55.90  
  7 purchase totals = $671.00       $716.8237   $716.82   $716.75   $716.90