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 $241.68   3.794%   $250.8493   $250.85   $250.85   $250.80  
  Purchase #2 $144.55   13.152%   $163.5612   $163.56   $163.55   $163.60  
  Purchase #3 $27.64   11.448%   $30.8042   $30.80   $30.80   $30.80  
  Purchase #4 $203.48   6.760%   $217.2352   $217.24   $217.25   $217.20  
  Purchase #5 $167.50   12.221%   $187.9702   $187.97   $187.95   $188.00  
  Purchase #6 $235.68   5.382%   $248.3643   $248.36   $248.35   $248.40  
  Purchase #7 $239.40   6.723%   $255.4949   $255.49   $255.50   $255.50  
  7 purchase totals = $1,259.93       $1,354.2793   $1,354.27   $1,354.25   $1,354.30