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 $105.41   12.527%   $118.6147   $118.61   $118.60   $118.60  
  Purchase #2 $77.82   5.506%   $82.1048   $82.10   $82.10   $82.10  
  Purchase #3 $79.94   5.276%   $84.1576   $84.16   $84.15   $84.20  
  Purchase #4 $118.46   11.836%   $132.4809   $132.48   $132.50   $132.50  
  Purchase #5 $25.93   5.154%   $27.2664   $27.27   $27.25   $27.30  
  Purchase #6 $104.97   13.525%   $119.1672   $119.17   $119.15   $119.20  
  Purchase #7 $169.56   12.863%   $191.3705   $191.37   $191.35   $191.40  
  7 purchase totals = $682.09       $755.1621   $755.16   $755.10   $755.30