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 $54.97   10.190%   $60.5714   $60.57   $60.55   $60.60  
  Purchase #2 $33.47   3.402%   $34.6086   $34.61   $34.60   $34.60  
  Purchase #3 $156.71   7.686%   $168.7547   $168.75   $168.75   $168.80  
  Purchase #4 $15.59   6.395%   $16.587   $16.59   $16.60   $16.60  
  Purchase #5 $13.72   12.223%   $15.397   $15.40   $15.40   $15.40  
  Purchase #6 $117.62   7.169%   $126.0522   $126.05   $126.05   $126.10  
  Purchase #7 $194.45   10.359%   $214.5931   $214.59   $214.60   $214.60  
  7 purchase totals = $586.53       $636.5640   $636.56   $636.55   $636.70