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 $24.86   3.274%   $25.6739   $25.67   $25.65   $25.70  
  Purchase #2 $101.91   12.235%   $114.3787   $114.38   $114.40   $114.40  
  Purchase #3 $57.96   8.543%   $62.9115   $62.91   $62.90   $62.90  
  Purchase #4 $16.69   8.850%   $18.1671   $18.17   $18.15   $18.20  
  Purchase #5 $73.32   3.200%   $75.6662   $75.67   $75.65   $75.70  
  Purchase #6 $25.89   8.412%   $28.0679   $28.07   $28.05   $28.10  
  Purchase #7 $47.86   8.424%   $51.8917   $51.89   $51.90   $51.90  
  7 purchase totals = $348.49       $376.7570   $376.76   $376.70   $376.90