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 $234.95   5.721%   $248.3915   $248.39   $248.40   $248.40  
  Purchase #2 $246.61   12.103%   $276.4572   $276.46   $276.45   $276.50  
  Purchase #3 $98.36   6.441%   $104.6954   $104.70   $104.70   $104.70  
  Purchase #4 $207.95   5.121%   $218.5991   $218.60   $218.60   $218.60  
  Purchase #5 $130.93   7.608%   $140.8912   $140.89   $140.90   $140.90  
  Purchase #6 $59.98   6.851%   $64.0892   $64.09   $64.10   $64.10  
  Purchase #7 $140.77   5.273%   $148.1928   $148.19   $148.20   $148.20  
  7 purchase totals = $1,119.55       $1,201.3164   $1,201.32   $1,201.35   $1,201.40