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 $24.77   6.530%   $26.3875   $26.39   $26.40   $26.40  
  Purchase #2 $164.63   3.834%   $170.9419   $170.94   $170.95   $170.90  
  Purchase #3 $61.38   12.280%   $68.9175   $68.92   $68.90   $68.90  
  Purchase #4 $246.51   11.680%   $275.3024   $275.30   $275.30   $275.30  
  Purchase #5 $106.26   8.409%   $115.1954   $115.20   $115.20   $115.20  
  Purchase #6 $174.89   6.749%   $186.6933   $186.69   $186.70   $186.70  
  Purchase #7 $142.25   6.277%   $151.179   $151.18   $151.20   $151.20  
  7 purchase totals = $920.69       $994.6170   $994.62   $994.65   $994.60