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 $115.50   5.859%   $122.2671   $122.27   $122.25   $122.30  
  Purchase #2 $247.82   6.454%   $263.8143   $263.81   $263.80   $263.80  
  Purchase #3 $18.89   6.182%   $20.0578   $20.06   $20.05   $20.10  
  Purchase #4 $168.56   5.159%   $177.256   $177.26   $177.25   $177.30  
  Purchase #5 $38.37   6.324%   $40.7965   $40.80   $40.80   $40.80  
  Purchase #6 $246.75   6.324%   $262.3545   $262.35   $262.35   $262.40  
  Purchase #7 $40.28   5.528%   $42.5067   $42.51   $42.50   $42.50  
  7 purchase totals = $876.17       $929.0529   $929.06   $929.00   $929.20