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 $114.47   6.772%   $122.2219   $122.22   $122.20   $122.20  
  Purchase #2 $110.25   12.208%   $123.7093   $123.71   $123.70   $123.70  
  Purchase #3 $104.99   9.259%   $114.711   $114.71   $114.70   $114.70  
  Purchase #4 $23.39   8.569%   $25.3943   $25.39   $25.40   $25.40  
  Purchase #5 $52.67   11.704%   $58.8345   $58.83   $58.85   $58.80  
  Purchase #6 $236.26   8.571%   $256.5098   $256.51   $256.50   $256.50  
  Purchase #7 $159.80   10.293%   $176.2482   $176.25   $176.25   $176.20  
  7 purchase totals = $801.83       $877.6290   $877.62   $877.60   $877.50