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 $228.26   11.221%   $253.8731   $253.87   $253.85   $253.90  
  Purchase #2 $214.31   9.296%   $234.2323   $234.23   $234.25   $234.20  
  Purchase #3 $154.31   11.293%   $171.7362   $171.74   $171.75   $171.70  
  Purchase #4 $240.50   11.527%   $268.2224   $268.22   $268.20   $268.20  
  Purchase #5 $24.97   5.257%   $26.2827   $26.28   $26.30   $26.30  
  Purchase #6 $230.94   10.686%   $255.6182   $255.62   $255.60   $255.60  
  Purchase #7 $113.40   7.184%   $121.5467   $121.55   $121.55   $121.50  
  7 purchase totals = $1,206.69       $1,331.5116   $1,331.51   $1,331.50   $1,331.40