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 $23.41   13.578%   $26.5886   $26.59   $26.60   $26.60  
  Purchase #2 $76.85   8.353%   $83.2693   $83.27   $83.25   $83.30  
  Purchase #3 $51.63   4.726%   $54.07   $54.07   $54.05   $54.10  
  Purchase #4 $9.61   7.849%   $10.3643   $10.36   $10.35   $10.40  
  Purchase #5 $240.68   4.327%   $251.0942   $251.09   $251.10   $251.10  
  Purchase #6 $58.38   8.251%   $63.1969   $63.20   $63.20   $63.20  
  Purchase #7 $6.57   10.151%   $7.2369   $7.24   $7.25   $7.20  
  7 purchase totals = $467.13       $495.8202   $495.82   $495.80   $495.90