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 $135.64   7.680%   $146.0572   $146.06   $146.05   $146.10  
  Purchase #2 $61.28   7.596%   $65.9348   $65.93   $65.95   $65.90  
  Purchase #3 $134.48   6.266%   $142.9065   $142.91   $142.90   $142.90  
  Purchase #4 $138.76   10.382%   $153.1661   $153.17   $153.15   $153.20  
  Purchase #5 $99.54   6.419%   $105.9295   $105.93   $105.95   $105.90  
  Purchase #6 $223.81   8.503%   $242.8406   $242.84   $242.85   $242.80  
  Purchase #7 $58.31   10.269%   $64.2979   $64.30   $64.30   $64.30  
  7 purchase totals = $851.82       $921.1326   $921.14   $921.15   $921.10