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 $38.95   13.271%   $44.1191   $44.12   $44.10   $44.10  
  Purchase #2 $236.83   11.265%   $263.5089   $263.51   $263.50   $263.50  
  Purchase #3 $134.42   10.119%   $148.022   $148.02   $148.00   $148.00  
  Purchase #4 $197.27   9.853%   $216.707   $216.71   $216.70   $216.70  
  Purchase #5 $234.48   7.757%   $252.6686   $252.67   $252.65   $252.70  
  Purchase #6 $198.29   7.677%   $213.5127   $213.51   $213.50   $213.50  
  Purchase #7 $121.50   13.482%   $137.8806   $137.88   $137.90   $137.90  
  7 purchase totals = $1,161.74       $1,276.4189   $1,276.42   $1,276.35   $1,276.40