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 $239.66   9.680%   $262.8591   $262.86   $262.85   $262.90  
  Purchase #2 $33.62   12.213%   $37.726   $37.73   $37.75   $37.70  
  Purchase #3 $26.74   4.129%   $27.8441   $27.84   $27.85   $27.80  
  Purchase #4 $222.38   5.420%   $234.433   $234.43   $234.45   $234.40  
  Purchase #5 $16.90   4.103%   $17.5934   $17.59   $17.60   $17.60  
  Purchase #6 $167.91   6.416%   $178.6831   $178.68   $178.70   $178.70  
  Purchase #7 $168.46   13.861%   $191.8102   $191.81   $191.80   $191.80  
  7 purchase totals = $875.67       $950.9489   $950.94   $951.00   $950.90