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 $242.88   12.198%   $272.5065   $272.51   $272.50   $272.50  
  Purchase #2 $216.72   11.644%   $241.9549   $241.95   $241.95   $242.00  
  Purchase #3 $148.66   5.393%   $156.6772   $156.68   $156.70   $156.70  
  Purchase #4 $146.39   3.628%   $151.701   $151.70   $151.70   $151.70  
  Purchase #5 $112.95   5.171%   $118.7906   $118.79   $118.80   $118.80  
  Purchase #6 $197.71   8.647%   $214.806   $214.81   $214.80   $214.80  
  Purchase #7 $61.46   8.382%   $66.6116   $66.61   $66.60   $66.60  
  7 purchase totals = $1,126.77       $1,223.0478   $1,223.05   $1,223.05   $1,223.10