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 $63.49   4.272%   $66.2023   $66.20   $66.20   $66.20  
  Purchase #2 $234.80   5.452%   $247.6013   $247.60   $247.60   $247.60  
  Purchase #3 $217.69   5.647%   $229.983   $229.98   $230.00   $230.00  
  Purchase #4 $131.51   3.688%   $136.3601   $136.36   $136.35   $136.40  
  Purchase #5 $78.63   11.255%   $87.4798   $87.48   $87.50   $87.50  
  Purchase #6 $11.94   3.860%   $12.4009   $12.40   $12.40   $12.40  
  Purchase #7 $138.30   6.106%   $146.7446   $146.74   $146.75   $146.70  
  7 purchase totals = $876.36       $926.7720   $926.76   $926.80   $926.80