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 $175.65   7.390%   $188.6305   $188.63   $188.65   $188.60  
  Purchase #2 $53.51   5.870%   $56.651   $56.65   $56.65   $56.70  
  Purchase #3 $59.63   11.362%   $66.4052   $66.41   $66.40   $66.40  
  Purchase #4 $74.34   5.652%   $78.5417   $78.54   $78.55   $78.50  
  Purchase #5 $95.70   6.181%   $101.6152   $101.62   $101.60   $101.60  
  Purchase #6 $237.85   4.684%   $248.9909   $248.99   $249.00   $249.00  
  Purchase #7 $23.90   3.600%   $24.7604   $24.76   $24.75   $24.80  
  7 purchase totals = $720.58       $765.5949   $765.60   $765.60   $765.60