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 $25.69   6.667%   $27.4028   $27.40   $27.40   $27.40  
  Purchase #2 $198.99   3.424%   $205.8034   $205.80   $205.80   $205.80  
  Purchase #3 $65.36   13.269%   $74.0326   $74.03   $74.05   $74.00  
  Purchase #4 $104.64   7.531%   $112.5204   $112.52   $112.50   $112.50  
  Purchase #5 $23.81   9.635%   $26.1041   $26.10   $26.10   $26.10  
  Purchase #6 $245.91   6.382%   $261.604   $261.60   $261.60   $261.60  
  Purchase #7 $16.66   3.215%   $17.1956   $17.20   $17.20   $17.20  
  7 purchase totals = $681.06       $724.6629   $724.65   $724.65   $724.60