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 $184.82   10.712%   $204.6179   $204.62   $204.60   $204.60  
  Purchase #2 $163.82   11.855%   $183.2409   $183.24   $183.25   $183.20  
  Purchase #3 $133.35   10.189%   $146.937   $146.94   $146.95   $146.90  
  Purchase #4 $195.25   6.403%   $207.7519   $207.75   $207.75   $207.80  
  Purchase #5 $12.59   6.716%   $13.4355   $13.44   $13.45   $13.40  
  Purchase #6 $190.32   10.692%   $210.669   $210.67   $210.65   $210.70  
  Purchase #7 $72.51   6.382%   $77.1376   $77.14   $77.15   $77.10  
  7 purchase totals = $952.66       $1,043.7898   $1,043.80   $1,043.80   $1,043.70