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 $89.69   10.297%   $98.9254   $98.93   $98.95   $98.90  
  Purchase #2 $167.55   11.522%   $186.8551   $186.86   $186.85   $186.90  
  Purchase #3 $125.95   13.476%   $142.923   $142.92   $142.90   $142.90  
  Purchase #4 $189.71   9.475%   $207.685   $207.69   $207.70   $207.70  
  Purchase #5 $46.81   6.409%   $49.8101   $49.81   $49.80   $49.80  
  Purchase #6 $53.57   6.498%   $57.051   $57.05   $57.05   $57.10  
  Purchase #7 $188.40   10.701%   $208.5607   $208.56   $208.55   $208.60  
  7 purchase totals = $861.68       $951.8103   $951.82   $951.80   $951.90