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 $60.74   7.396%   $65.2323   $65.23   $65.25   $65.20  
  Purchase #2 $60.53   9.868%   $66.5031   $66.50   $66.50   $66.50  
  Purchase #3 $17.76   7.206%   $19.0398   $19.04   $19.05   $19.00  
  Purchase #4 $49.94   8.698%   $54.2838   $54.28   $54.30   $54.30  
  Purchase #5 $6.88   8.617%   $7.4728   $7.47   $7.45   $7.50  
  Purchase #6 $126.83   3.276%   $130.985   $130.99   $131.00   $131.00  
  Purchase #7 $177.51   5.344%   $186.9961   $187.00   $187.00   $187.00  
  7 purchase totals = $500.19       $530.5129   $530.51   $530.55   $530.50