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 $227.28   10.462%   $251.058   $251.06   $251.05   $251.10  
  Purchase #2 $31.69   10.214%   $34.9268   $34.93   $34.95   $34.90  
  Purchase #3 $135.78   4.131%   $141.3891   $141.39   $141.40   $141.40  
  Purchase #4 $63.82   10.600%   $70.5849   $70.58   $70.60   $70.60  
  Purchase #5 $183.94   6.851%   $196.5417   $196.54   $196.55   $196.50  
  Purchase #6 $166.41   13.527%   $188.9203   $188.92   $188.90   $188.90  
  Purchase #7 $73.51   10.568%   $81.2785   $81.28   $81.30   $81.30  
  7 purchase totals = $882.43       $964.6993   $964.70   $964.75   $964.70