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 $23.61   10.305%   $26.043   $26.04   $26.05   $26.00  
  Purchase #2 $157.59   3.613%   $163.2837   $163.28   $163.30   $163.30  
  Purchase #3 $78.57   12.810%   $88.6348   $88.63   $88.65   $88.60  
  Purchase #4 $178.37   9.605%   $195.5024   $195.50   $195.50   $195.50  
  Purchase #5 $81.58   9.393%   $89.2428   $89.24   $89.25   $89.20  
  Purchase #6 $178.77   9.482%   $195.721   $195.72   $195.70   $195.70  
  Purchase #7 $117.78   13.634%   $133.8381   $133.84   $133.85   $133.80  
  7 purchase totals = $816.27       $892.2658   $892.25   $892.30   $892.10