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 $117.80   6.524%   $125.4853   $125.49   $125.50   $125.50  
  Purchase #2 $246.89   10.703%   $273.3146   $273.31   $273.30   $273.30  
  Purchase #3 $160.54   11.855%   $179.572   $179.57   $179.55   $179.60  
  Purchase #4 $78.94   5.849%   $83.5572   $83.56   $83.55   $83.60  
  Purchase #5 $190.97   12.805%   $215.4237   $215.42   $215.40   $215.40  
  Purchase #6 $171.73   3.793%   $178.2437   $178.24   $178.25   $178.20  
  Purchase #7 $236.34   9.117%   $257.8871   $257.89   $257.90   $257.90  
  7 purchase totals = $1,203.21       $1,313.4836   $1,313.48   $1,313.45   $1,313.50