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 $24.53   4.359%   $25.5993   $25.60   $25.60   $25.60  
  Purchase #2 $167.67   12.617%   $188.8249   $188.82   $188.80   $188.80  
  Purchase #3 $73.53   8.337%   $79.6602   $79.66   $79.65   $79.70  
  Purchase #4 $163.86   6.865%   $175.109   $175.11   $175.10   $175.10  
  Purchase #5 $32.93   8.419%   $35.7024   $35.70   $35.70   $35.70  
  Purchase #6 $71.84   7.643%   $77.3307   $77.33   $77.35   $77.30  
  Purchase #7 $41.71   10.425%   $46.0583   $46.06   $46.05   $46.10  
  7 purchase totals = $576.07       $628.2848   $628.28   $628.25   $628.30