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 $117.99   6.584%   $125.7585   $125.76   $125.75   $125.80  
  Purchase #2 $144.63   8.430%   $156.8223   $156.82   $156.80   $156.80  
  Purchase #3 $14.61   6.286%   $15.5284   $15.53   $15.55   $15.50  
  Purchase #4 $191.95   6.638%   $204.6916   $204.69   $204.70   $204.70  
  Purchase #5 $24.50   4.849%   $25.688   $25.69   $25.70   $25.70  
  Purchase #6 $231.69   11.401%   $258.105   $258.11   $258.10   $258.10  
  Purchase #7 $181.96   4.736%   $190.5776   $190.58   $190.60   $190.60  
  7 purchase totals = $907.33       $977.1714   $977.18   $977.20   $977.20