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 $60.25   8.271%   $65.2333   $65.23   $65.25   $65.20  
  Purchase #2 $31.87   13.258%   $36.0953   $36.10   $36.10   $36.10  
  Purchase #3 $233.87   7.232%   $250.7835   $250.78   $250.80   $250.80  
  Purchase #4 $213.95   13.127%   $242.0352   $242.04   $242.05   $242.00  
  Purchase #5 $250.61   6.874%   $267.8369   $267.84   $267.85   $267.80  
  Purchase #6 $136.93   8.806%   $148.9881   $148.99   $149.00   $149.00  
  Purchase #7 $69.27   7.853%   $74.7098   $74.71   $74.70   $74.70  
  7 purchase totals = $996.75       $1,085.6821   $1,085.69   $1,085.75   $1,085.60