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 $243.49   9.434%   $266.4608   $266.46   $266.45   $266.50  
  Purchase #2 $168.35   4.479%   $175.8904   $175.89   $175.90   $175.90  
  Purchase #3 $78.57   6.609%   $83.7627   $83.76   $83.75   $83.80  
  Purchase #4 $12.97   10.671%   $14.354   $14.35   $14.35   $14.40  
  Purchase #5 $59.72   10.486%   $65.9822   $65.98   $66.00   $66.00  
  Purchase #6 $205.75   9.119%   $224.5123   $224.51   $224.50   $224.50  
  Purchase #7 $115.55   11.397%   $128.7192   $128.72   $128.70   $128.70  
  7 purchase totals = $884.40       $959.6816   $959.67   $959.65   $959.80