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 $58.63   4.390%   $61.2039   $61.20   $61.20   $61.20  
  Purchase #2 $228.38   13.154%   $258.4211   $258.42   $258.40   $258.40  
  Purchase #3 $86.36   8.699%   $93.8725   $93.87   $93.85   $93.90  
  Purchase #4 $203.73   13.728%   $231.6981   $231.70   $231.70   $231.70  
  Purchase #5 $32.69   3.681%   $33.8933   $33.89   $33.90   $33.90  
  Purchase #6 $243.98   12.822%   $275.2631   $275.26   $275.25   $275.30  
  Purchase #7 $97.87   9.720%   $107.383   $107.38   $107.40   $107.40  
  7 purchase totals = $951.64       $1,061.7350   $1,061.72   $1,061.70   $1,061.80