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 $183.75   13.215%   $208.0326   $208.03   $208.05   $208.00  
  Purchase #2 $60.46   10.863%   $67.0278   $67.03   $67.05   $67.00  
  Purchase #3 $30.50   10.718%   $33.769   $33.77   $33.75   $33.80  
  Purchase #4 $158.50   9.822%   $174.0679   $174.07   $174.05   $174.10  
  Purchase #5 $127.60   6.796%   $136.2717   $136.27   $136.25   $136.30  
  Purchase #6 $216.48   12.638%   $243.8387   $243.84   $243.85   $243.80  
  Purchase #7 $213.27   6.411%   $226.9427   $226.94   $226.95   $226.90  
  7 purchase totals = $990.56       $1,089.9504   $1,089.95   $1,089.95   $1,089.90