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 $24.26   6.865%   $25.9254   $25.93   $25.95   $25.90  
  Purchase #2 $50.68   7.753%   $54.6092   $54.61   $54.60   $54.60  
  Purchase #3 $38.85   10.406%   $42.8927   $42.89   $42.90   $42.90  
  Purchase #4 $125.35   4.271%   $130.7037   $130.70   $130.70   $130.70  
  Purchase #5 $60.93   13.667%   $69.2573   $69.26   $69.25   $69.30  
  Purchase #6 $250.87   12.726%   $282.7957   $282.80   $282.80   $282.80  
  Purchase #7 $130.32   9.843%   $143.1474   $143.15   $143.15   $143.10  
  7 purchase totals = $681.26       $749.3314   $749.34   $749.35   $749.30