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 $23.56   4.732%   $24.6749   $24.67   $24.65   $24.70  
  Purchase #2 $249.61   11.186%   $277.5314   $277.53   $277.55   $277.50  
  Purchase #3 $98.71   5.271%   $103.913   $103.91   $103.90   $103.90  
  Purchase #4 $200.50   6.803%   $214.14   $214.14   $214.15   $214.10  
  Purchase #5 $43.36   7.150%   $46.4602   $46.46   $46.45   $46.50  
  Purchase #6 $51.53   11.716%   $57.5673   $57.57   $57.55   $57.60  
  Purchase #7 $182.69   8.417%   $198.067   $198.07   $198.05   $198.10  
  7 purchase totals = $849.96       $922.3538   $922.35   $922.30   $922.40