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 $46.65   6.487%   $49.6762   $49.68   $49.70   $49.70  
  Purchase #2 $107.97   6.739%   $115.2461   $115.25   $115.25   $115.20  
  Purchase #3 $132.98   7.824%   $143.3844   $143.38   $143.40   $143.40  
  Purchase #4 $178.75   11.172%   $198.72   $198.72   $198.70   $198.70  
  Purchase #5 $168.28   4.530%   $175.9031   $175.90   $175.90   $175.90  
  Purchase #6 $242.59   3.266%   $250.513   $250.51   $250.50   $250.50  
  Purchase #7 $110.92   12.387%   $124.6597   $124.66   $124.65   $124.70  
  7 purchase totals = $988.14       $1,058.1025   $1,058.10   $1,058.10   $1,058.10