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 $58.74   7.834%   $63.3417   $63.34   $63.35   $63.30  
  Purchase #2 $36.57   5.149%   $38.453   $38.45   $38.45   $38.50  
  Purchase #3 $68.36   5.748%   $72.2893   $72.29   $72.30   $72.30  
  Purchase #4 $79.40   6.868%   $84.8532   $84.85   $84.85   $84.90  
  Purchase #5 $207.58   3.443%   $214.727   $214.73   $214.75   $214.70  
  Purchase #6 $175.69   5.517%   $185.3828   $185.38   $185.40   $185.40  
  Purchase #7 $22.33   3.758%   $23.1692   $23.17   $23.15   $23.20  
  7 purchase totals = $648.67       $682.2162   $682.21   $682.25   $682.30