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 $243.26   8.539%   $264.032   $264.03   $264.05   $264.00  
  Purchase #2 $230.70   13.482%   $261.803   $261.80   $261.80   $261.80  
  Purchase #3 $106.93   10.787%   $118.4645   $118.46   $118.45   $118.50  
  Purchase #4 $187.44   5.576%   $197.8917   $197.89   $197.90   $197.90  
  Purchase #5 $231.45   13.517%   $262.7351   $262.74   $262.75   $262.70  
  Purchase #6 $229.29   3.852%   $238.1223   $238.12   $238.10   $238.10  
  Purchase #7 $241.30   3.136%   $248.8672   $248.87   $248.85   $248.90  
  7 purchase totals = $1,470.37       $1,591.9158   $1,591.91   $1,591.90   $1,591.90