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 $23.55   12.792%   $26.5625   $26.56   $26.55   $26.60  
  Purchase #2 $98.29   5.141%   $103.3431   $103.34   $103.35   $103.30  
  Purchase #3 $157.64   10.334%   $173.9305   $173.93   $173.95   $173.90  
  Purchase #4 $60.80   4.679%   $63.6448   $63.64   $63.65   $63.60  
  Purchase #5 $143.53   5.670%   $151.6682   $151.67   $151.65   $151.70  
  Purchase #6 $64.55   13.296%   $73.1326   $73.13   $73.15   $73.10  
  Purchase #7 $140.69   9.576%   $154.1625   $154.16   $154.15   $154.20  
  7 purchase totals = $689.05       $746.4442   $746.43   $746.45   $746.40