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 $63.81   5.257%   $67.1645   $67.16   $67.15   $67.20  
  Purchase #2 $250.80   10.672%   $277.5654   $277.57   $277.55   $277.60  
  Purchase #3 $116.99   7.545%   $125.8169   $125.82   $125.80   $125.80  
  Purchase #4 $36.68   9.794%   $40.2724   $40.27   $40.25   $40.30  
  Purchase #5 $140.62   10.538%   $155.4385   $155.44   $155.45   $155.40  
  Purchase #6 $50.72   8.433%   $54.9972   $55.00   $55.00   $55.00  
  Purchase #7 $250.70   10.111%   $276.0483   $276.05   $276.05   $276.00  
  7 purchase totals = $910.32       $997.3032   $997.31   $997.25   $997.30