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 $226.37   11.121%   $251.5446   $251.54   $251.55   $251.50  
  Purchase #2 $237.67   12.336%   $266.989   $266.99   $267.00   $267.00  
  Purchase #3 $227.78   8.617%   $247.4078   $247.41   $247.40   $247.40  
  Purchase #4 $157.97   3.726%   $163.856   $163.86   $163.85   $163.90  
  Purchase #5 $47.70   13.858%   $54.3103   $54.31   $54.30   $54.30  
  Purchase #6 $241.63   11.151%   $268.5742   $268.57   $268.55   $268.60  
  Purchase #7 $38.25   6.328%   $40.6705   $40.67   $40.65   $40.70  
  7 purchase totals = $1,177.37       $1,293.3524   $1,293.35   $1,293.30   $1,293.40