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 $181.56   9.569%   $198.9335   $198.93   $198.95   $198.90  
  Purchase #2 $95.99   13.248%   $108.7068   $108.71   $108.70   $108.70  
  Purchase #3 $154.50   11.848%   $172.8052   $172.81   $172.80   $172.80  
  Purchase #4 $228.80   9.237%   $249.9343   $249.93   $249.95   $249.90  
  Purchase #5 $85.62   10.474%   $94.5878   $94.59   $94.60   $94.60  
  Purchase #6 $58.83   6.563%   $62.691   $62.69   $62.70   $62.70  
  Purchase #7 $60.61   4.815%   $63.5284   $63.53   $63.55   $63.50  
  7 purchase totals = $865.91       $951.1870   $951.19   $951.25   $951.10