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 $84.68   8.288%   $91.6983   $91.70   $91.70   $91.70  
  Purchase #2 $226.47   8.291%   $245.2466   $245.25   $245.25   $245.20  
  Purchase #3 $51.38   12.398%   $57.7501   $57.75   $57.75   $57.80  
  Purchase #4 $232.55   12.520%   $261.6653   $261.67   $261.65   $261.70  
  Purchase #5 $95.51   5.641%   $100.8977   $100.90   $100.90   $100.90  
  Purchase #6 $155.30   4.837%   $162.8119   $162.81   $162.80   $162.80  
  Purchase #7 $247.68   10.114%   $272.7304   $272.73   $272.75   $272.70  
  7 purchase totals = $1,093.57       $1,192.8003   $1,192.81   $1,192.80   $1,192.80