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 $60.99   4.687%   $63.8486   $63.85   $63.85   $63.80  
  Purchase #2 $249.88   9.716%   $274.1583   $274.16   $274.15   $274.20  
  Purchase #3 $23.54   13.715%   $26.7685   $26.77   $26.75   $26.80  
  Purchase #4 $110.53   13.141%   $125.0547   $125.05   $125.05   $125.10  
  Purchase #5 $50.69   12.768%   $57.1621   $57.16   $57.15   $57.20  
  Purchase #6 $211.55   6.600%   $225.5123   $225.51   $225.50   $225.50  
  Purchase #7 $165.25   13.318%   $187.258   $187.26   $187.25   $187.30  
  7 purchase totals = $872.43       $959.7625   $959.76   $959.70   $959.90