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 $241.91   10.417%   $267.1098   $267.11   $267.10   $267.10  
  Purchase #2 $30.65   6.659%   $32.691   $32.69   $32.70   $32.70  
  Purchase #3 $247.80   5.595%   $261.6644   $261.66   $261.65   $261.70  
  Purchase #4 $68.93   13.559%   $78.2762   $78.28   $78.30   $78.30  
  Purchase #5 $198.71   8.215%   $215.034   $215.03   $215.05   $215.00  
  Purchase #6 $53.92   7.583%   $58.0088   $58.01   $58.00   $58.00  
  Purchase #7 $211.42   13.343%   $239.6298   $239.63   $239.65   $239.60  
  7 purchase totals = $1,053.34       $1,152.4140   $1,152.41   $1,152.45   $1,152.40