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 $87.38   12.596%   $98.3864   $98.39   $98.40   $98.40  
  Purchase #2 $64.40   13.662%   $73.1983   $73.20   $73.20   $73.20  
  Purchase #3 $134.61   12.864%   $151.9262   $151.93   $151.95   $151.90  
  Purchase #4 $48.99   7.303%   $52.5677   $52.57   $52.55   $52.60  
  Purchase #5 $43.96   6.267%   $46.715   $46.72   $46.70   $46.70  
  Purchase #6 $127.65   13.276%   $144.5968   $144.60   $144.60   $144.60  
  Purchase #7 $25.25   5.457%   $26.6279   $26.63   $26.65   $26.60  
  7 purchase totals = $532.24       $594.0183   $594.04   $594.05   $594.00