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 $92.68   6.291%   $98.5105   $98.51   $98.50   $98.50  
  Purchase #2 $55.34   8.794%   $60.2066   $60.21   $60.20   $60.20  
  Purchase #3 $78.41   8.184%   $84.8271   $84.83   $84.85   $84.80  
  Purchase #4 $49.37   5.463%   $52.0671   $52.07   $52.05   $52.10  
  Purchase #5 $38.81   12.675%   $43.7292   $43.73   $43.75   $43.70  
  Purchase #6 $16.28   13.618%   $18.497   $18.50   $18.50   $18.50  
  Purchase #7 $131.62   5.140%   $138.3853   $138.39   $138.40   $138.40  
  7 purchase totals = $462.51       $496.2228   $496.24   $496.25   $496.20