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 $246.72   6.174%   $261.9525   $261.95   $261.95   $262.00  
  Purchase #2 $133.80   7.613%   $143.9862   $143.99   $144.00   $144.00  
  Purchase #3 $225.42   10.689%   $249.5151   $249.52   $249.50   $249.50  
  Purchase #4 $15.27   4.226%   $15.9153   $15.92   $15.90   $15.90  
  Purchase #5 $186.91   7.858%   $201.5974   $201.60   $201.60   $201.60  
  Purchase #6 $86.91   12.776%   $98.0136   $98.01   $98.00   $98.00  
  Purchase #7 $148.74   9.234%   $162.4747   $162.47   $162.45   $162.50  
  7 purchase totals = $1,043.77       $1,133.4548   $1,133.46   $1,133.40   $1,133.50