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 $117.85   6.796%   $125.8591   $125.86   $125.85   $125.90  
  Purchase #2 $237.86   3.565%   $246.3397   $246.34   $246.35   $246.30  
  Purchase #3 $17.75   8.454%   $19.2506   $19.25   $19.25   $19.30  
  Purchase #4 $234.36   11.549%   $261.4262   $261.43   $261.45   $261.40  
  Purchase #5 $160.47   10.486%   $177.2969   $177.30   $177.30   $177.30  
  Purchase #6 $45.30   9.190%   $49.4631   $49.46   $49.45   $49.50  
  Purchase #7 $246.30   5.505%   $259.8588   $259.86   $259.85   $259.90  
  7 purchase totals = $1,059.89       $1,139.4944   $1,139.50   $1,139.50   $1,139.60