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 $112.26   13.797%   $127.7485   $127.75   $127.75   $127.70  
  Purchase #2 $248.73   3.601%   $257.6868   $257.69   $257.70   $257.70  
  Purchase #3 $222.54   4.568%   $232.7056   $232.71   $232.70   $232.70  
  Purchase #4 $174.62   8.556%   $189.5605   $189.56   $189.55   $189.60  
  Purchase #5 $84.97   5.457%   $89.6068   $89.61   $89.60   $89.60  
  Purchase #6 $82.78   3.346%   $85.5498   $85.55   $85.55   $85.50  
  Purchase #7 $33.28   8.137%   $35.988   $35.99   $36.00   $36.00  
  7 purchase totals = $959.18       $1,018.8460   $1,018.86   $1,018.85   $1,018.80