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 $230.61   13.285%   $261.2465   $261.25   $261.25   $261.20  
  Purchase #2 $212.82   9.564%   $233.1741   $233.17   $233.15   $233.20  
  Purchase #3 $36.67   5.555%   $38.707   $38.71   $38.70   $38.70  
  Purchase #4 $164.35   6.558%   $175.1281   $175.13   $175.15   $175.10  
  Purchase #5 $231.37   5.276%   $243.5771   $243.58   $243.60   $243.60  
  Purchase #6 $80.96   9.328%   $88.5119   $88.51   $88.50   $88.50  
  Purchase #7 $174.90   6.753%   $186.711   $186.71   $186.70   $186.70  
  7 purchase totals = $1,131.68       $1,227.0557   $1,227.06   $1,227.05   $1,227.00