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 $139.48   10.670%   $154.3625   $154.36   $154.35   $154.40  
  Purchase #2 $163.86   9.684%   $179.7282   $179.73   $179.75   $179.70  
  Purchase #3 $164.48   13.370%   $186.471   $186.47   $186.45   $186.50  
  Purchase #4 $30.77   12.794%   $34.7067   $34.71   $34.70   $34.70  
  Purchase #5 $226.94   6.810%   $242.3946   $242.39   $242.40   $242.40  
  Purchase #6 $152.40   9.171%   $166.3766   $166.38   $166.40   $166.40  
  Purchase #7 $157.47   3.372%   $162.7799   $162.78   $162.80   $162.80  
  7 purchase totals = $1,035.40       $1,126.8195   $1,126.82   $1,126.85   $1,126.90