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 $153.53   7.259%   $164.6747   $164.67   $164.65   $164.70  
  Purchase #2 $216.34   4.555%   $226.1943   $226.19   $226.20   $226.20  
  Purchase #3 $177.70   6.202%   $188.721   $188.72   $188.70   $188.70  
  Purchase #4 $141.27   11.553%   $157.5909   $157.59   $157.60   $157.60  
  Purchase #5 $156.50   4.326%   $163.2702   $163.27   $163.25   $163.30  
  Purchase #6 $103.73   3.629%   $107.4944   $107.49   $107.50   $107.50  
  Purchase #7 $12.57   13.354%   $14.2486   $14.25   $14.25   $14.20  
  7 purchase totals = $961.64       $1,022.1941   $1,022.18   $1,022.15   $1,022.20