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 $60.55   10.322%   $66.8   $66.80   $66.80   $66.80  
  Purchase #2 $108.69   12.546%   $122.3262   $122.33   $122.35   $122.30  
  Purchase #3 $86.89   6.413%   $92.4623   $92.46   $92.45   $92.50  
  Purchase #4 $57.26   10.506%   $63.2757   $63.28   $63.30   $63.30  
  Purchase #5 $46.64   4.154%   $48.5774   $48.58   $48.60   $48.60  
  Purchase #6 $242.89   3.181%   $250.6163   $250.62   $250.60   $250.60  
  Purchase #7 $22.31   5.853%   $23.6158   $23.62   $23.60   $23.60  
  7 purchase totals = $625.23       $667.6737   $667.69   $667.70   $667.70