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 $164.69   13.382%   $186.7288   $186.73   $186.75   $186.70  
  Purchase #2 $240.69   6.861%   $257.2037   $257.20   $257.20   $257.20  
  Purchase #3 $41.33   12.801%   $46.6207   $46.62   $46.60   $46.60  
  Purchase #4 $247.26   6.659%   $263.725   $263.73   $263.75   $263.70  
  Purchase #5 $34.55   7.654%   $37.1945   $37.19   $37.20   $37.20  
  Purchase #6 $98.77   9.431%   $108.085   $108.09   $108.10   $108.10  
  Purchase #7 $26.95   9.371%   $29.4755   $29.48   $29.50   $29.50  
  7 purchase totals = $854.24       $929.0332   $929.04   $929.10   $929.00