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 $200.94   12.733%   $226.5257   $226.53   $226.55   $226.50  
  Purchase #2 $51.62   5.293%   $54.3522   $54.35   $54.35   $54.40  
  Purchase #3 $86.97   9.260%   $95.0234   $95.02   $95.00   $95.00  
  Purchase #4 $23.85   9.587%   $26.1365   $26.14   $26.15   $26.10  
  Purchase #5 $85.86   4.114%   $89.3923   $89.39   $89.40   $89.40  
  Purchase #6 $175.67   6.645%   $187.3433   $187.34   $187.35   $187.30  
  Purchase #7 $226.83   13.735%   $257.9851   $257.99   $258.00   $258.00  
  7 purchase totals = $851.74       $936.7585   $936.76   $936.80   $936.70