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 $101.40   8.186%   $109.7006   $109.70   $109.70   $109.70  
  Purchase #2 $119.45   5.353%   $125.8442   $125.84   $125.85   $125.80  
  Purchase #3 $195.36   9.638%   $214.1888   $214.19   $214.20   $214.20  
  Purchase #4 $32.60   5.360%   $34.3474   $34.35   $34.35   $34.30  
  Purchase #5 $82.35   10.807%   $91.2496   $91.25   $91.25   $91.20  
  Purchase #6 $195.39   8.835%   $212.6527   $212.65   $212.65   $212.70  
  Purchase #7 $155.61   12.272%   $174.7065   $174.71   $174.70   $174.70  
  7 purchase totals = $882.16       $962.6898   $962.69   $962.70   $962.60