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 $27.99   4.448%   $29.235   $29.24   $29.25   $29.20  
  Purchase #2 $24.51   4.237%   $25.5485   $25.55   $25.55   $25.50  
  Purchase #3 $193.48   7.874%   $208.7146   $208.71   $208.70   $208.70  
  Purchase #4 $142.49   8.117%   $154.0559   $154.06   $154.05   $154.10  
  Purchase #5 $113.71   8.215%   $123.0513   $123.05   $123.05   $123.10  
  Purchase #6 $160.43   4.395%   $167.4809   $167.48   $167.50   $167.50  
  Purchase #7 $79.81   6.703%   $85.1597   $85.16   $85.15   $85.20  
  7 purchase totals = $742.42       $793.2459   $793.25   $793.25   $793.30