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 $56.34   13.532%   $63.9639   $63.96   $63.95   $64.00  
  Purchase #2 $245.35   8.271%   $265.6429   $265.64   $265.65   $265.60  
  Purchase #3 $219.39   11.328%   $244.2425   $244.24   $244.25   $244.20  
  Purchase #4 $241.89   11.361%   $269.3711   $269.37   $269.35   $269.40  
  Purchase #5 $15.44   10.500%   $17.0612   $17.06   $17.05   $17.10  
  Purchase #6 $51.48   13.606%   $58.4844   $58.48   $58.50   $58.50  
  Purchase #7 $178.54   4.238%   $186.1065   $186.11   $186.10   $186.10  
  7 purchase totals = $1,008.43       $1,104.8725   $1,104.86   $1,104.85   $1,104.90