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 $23.58   11.174%   $26.2148   $26.21   $26.20   $26.20  
  Purchase #2 $45.38   9.250%   $49.5777   $49.58   $49.60   $49.60  
  Purchase #3 $74.36   13.117%   $84.1138   $84.11   $84.10   $84.10  
  Purchase #4 $103.27   11.127%   $114.7609   $114.76   $114.75   $114.80  
  Purchase #5 $38.28   3.543%   $39.6363   $39.64   $39.65   $39.60  
  Purchase #6 $112.89   12.436%   $126.929   $126.93   $126.95   $126.90  
  Purchase #7 $141.25   7.119%   $151.3056   $151.31   $151.30   $151.30  
  7 purchase totals = $539.01       $592.5381   $592.54   $592.55   $592.50