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 $53.79   10.192%   $59.2723   $59.27   $59.25   $59.30  
  Purchase #2 $77.45   8.685%   $84.1765   $84.18   $84.20   $84.20  
  Purchase #3 $140.68   4.171%   $146.5478   $146.55   $146.55   $146.50  
  Purchase #4 $203.29   12.189%   $228.069   $228.07   $228.05   $228.10  
  Purchase #5 $106.70   10.776%   $118.198   $118.20   $118.20   $118.20  
  Purchase #6 $247.83   5.396%   $261.2029   $261.20   $261.20   $261.20  
  Purchase #7 $40.30   6.401%   $42.8796   $42.88   $42.90   $42.90  
  7 purchase totals = $870.04       $940.3461   $940.35   $940.35   $940.40