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 $56.65   6.161%   $60.1402   $60.14   $60.15   $60.10  
  Purchase #2 $156.39   13.535%   $177.5574   $177.56   $177.55   $177.60  
  Purchase #3 $117.44   13.840%   $133.6937   $133.69   $133.70   $133.70  
  Purchase #4 $77.85   6.168%   $82.6518   $82.65   $82.65   $82.70  
  Purchase #5 $226.31   7.127%   $242.4391   $242.44   $242.45   $242.40  
  Purchase #6 $132.75   9.429%   $145.267   $145.27   $145.25   $145.30  
  Purchase #7 $112.44   4.862%   $117.9068   $117.91   $117.90   $117.90  
  7 purchase totals = $879.83       $959.6560   $959.66   $959.65   $959.70