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 $236.27   10.648%   $261.428   $261.43   $261.45   $261.40  
  Purchase #2 $12.99   6.741%   $13.8657   $13.87   $13.85   $13.90  
  Purchase #3 $234.90   7.672%   $252.9215   $252.92   $252.90   $252.90  
  Purchase #4 $136.41   7.226%   $146.267   $146.27   $146.25   $146.30  
  Purchase #5 $232.32   6.666%   $247.8065   $247.81   $247.80   $247.80  
  Purchase #6 $130.56   5.273%   $137.4444   $137.44   $137.45   $137.40  
  Purchase #7 $133.87   12.635%   $150.7845   $150.78   $150.80   $150.80  
  7 purchase totals = $1,117.32       $1,210.5176   $1,210.52   $1,210.50   $1,210.50