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 $24.61   3.775%   $25.539   $25.54   $25.55   $25.50  
  Purchase #2 $238.79   4.662%   $249.9224   $249.92   $249.90   $249.90  
  Purchase #3 $238.81   10.610%   $264.1477   $264.15   $264.15   $264.10  
  Purchase #4 $66.48   9.131%   $72.5503   $72.55   $72.55   $72.60  
  Purchase #5 $230.51   4.157%   $240.0923   $240.09   $240.10   $240.10  
  Purchase #6 $202.29   4.733%   $211.8644   $211.86   $211.85   $211.90  
  Purchase #7 $168.81   4.120%   $175.765   $175.77   $175.75   $175.80  
  7 purchase totals = $1,170.30       $1,239.8811   $1,239.88   $1,239.85   $1,239.90