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 $248.30   5.156%   $261.1023   $261.10   $261.10   $261.10  
  Purchase #2 $51.39   13.311%   $58.2305   $58.23   $58.25   $58.20  
  Purchase #3 $21.64   12.628%   $24.3727   $24.37   $24.35   $24.40  
  Purchase #4 $232.78   12.656%   $262.2406   $262.24   $262.25   $262.20  
  Purchase #5 $206.38   5.134%   $216.9755   $216.98   $217.00   $217.00  
  Purchase #6 $238.92   6.221%   $253.7832   $253.78   $253.80   $253.80  
  Purchase #7 $95.90   6.619%   $102.2476   $102.25   $102.25   $102.20  
  7 purchase totals = $1,095.31       $1,178.9524   $1,178.95   $1,179.00   $1,178.90