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 $59.63   9.555%   $65.3276   $65.33   $65.35   $65.30  
  Purchase #2 $146.96   11.786%   $164.2807   $164.28   $164.30   $164.30  
  Purchase #3 $66.61   5.725%   $70.4234   $70.42   $70.40   $70.40  
  Purchase #4 $165.45   3.124%   $170.6187   $170.62   $170.60   $170.60  
  Purchase #5 $249.72   6.790%   $266.676   $266.68   $266.70   $266.70  
  Purchase #6 $175.47   10.283%   $193.5136   $193.51   $193.50   $193.50  
  Purchase #7 $243.45   12.289%   $273.3676   $273.37   $273.35   $273.40  
  7 purchase totals = $1,107.29       $1,204.2076   $1,204.21   $1,204.20   $1,204.20