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 $24.97   6.283%   $26.5389   $26.54   $26.55   $26.50  
  Purchase #2 $232.67   4.335%   $242.7562   $242.76   $242.75   $242.80  
  Purchase #3 $81.26   12.118%   $91.1071   $91.11   $91.10   $91.10  
  Purchase #4 $183.71   7.330%   $197.1759   $197.18   $197.20   $197.20  
  Purchase #5 $156.88   9.540%   $171.8464   $171.85   $171.85   $171.80  
  Purchase #6 $56.73   6.874%   $60.6296   $60.63   $60.65   $60.60  
  Purchase #7 $73.70   10.386%   $81.3545   $81.35   $81.35   $81.40  
  7 purchase totals = $809.92       $871.4086   $871.42   $871.45   $871.40