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 $24.28   8.118%   $26.2511   $26.25   $26.25   $26.30  
  Purchase #2 $189.81   9.858%   $208.5215   $208.52   $208.50   $208.50  
  Purchase #3 $138.80   8.676%   $150.8423   $150.84   $150.85   $150.80  
  Purchase #4 $195.36   5.806%   $206.7026   $206.70   $206.70   $206.70  
  Purchase #5 $206.99   12.808%   $233.5013   $233.50   $233.50   $233.50  
  Purchase #6 $60.62   5.127%   $63.728   $63.73   $63.75   $63.70  
  Purchase #7 $97.40   6.748%   $103.9726   $103.97   $103.95   $104.00  
  7 purchase totals = $913.26       $993.5194   $993.51   $993.50   $993.50