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 $217.66   11.145%   $241.9182   $241.92   $241.90   $241.90  
  Purchase #2 $144.52   8.175%   $156.3345   $156.33   $156.35   $156.30  
  Purchase #3 $234.39   5.366%   $246.9674   $246.97   $246.95   $247.00  
  Purchase #4 $59.30   9.473%   $64.9175   $64.92   $64.90   $64.90  
  Purchase #5 $183.41   9.423%   $200.6927   $200.69   $200.70   $200.70  
  Purchase #6 $241.69   8.264%   $261.6633   $261.66   $261.65   $261.70  
  Purchase #7 $83.86   3.535%   $86.8245   $86.82   $86.80   $86.80  
  7 purchase totals = $1,164.83       $1,259.3181   $1,259.31   $1,259.25   $1,259.30