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 $208.75   8.696%   $226.9029   $226.90   $226.90   $226.90  
  Purchase #2 $22.39   5.783%   $23.6848   $23.68   $23.70   $23.70  
  Purchase #3 $56.26   5.571%   $59.3942   $59.39   $59.40   $59.40  
  Purchase #4 $33.49   6.654%   $35.7184   $35.72   $35.70   $35.70  
  Purchase #5 $142.98   3.374%   $147.8041   $147.80   $147.80   $147.80  
  Purchase #6 $60.81   6.508%   $64.7675   $64.77   $64.75   $64.80  
  Purchase #7 $209.63   4.125%   $218.2772   $218.28   $218.30   $218.30  
  7 purchase totals = $734.31       $776.5491   $776.54   $776.55   $776.60