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 $22.83   5.538%   $24.0943   $24.09   $24.10   $24.10  
  Purchase #2 $250.38   5.863%   $265.0598   $265.06   $265.05   $265.10  
  Purchase #3 $89.73   5.539%   $94.7001   $94.70   $94.70   $94.70  
  Purchase #4 $216.79   7.120%   $232.2254   $232.23   $232.25   $232.20  
  Purchase #5 $232.35   9.252%   $253.847   $253.85   $253.85   $253.80  
  Purchase #6 $63.78   6.528%   $67.9436   $67.94   $67.95   $67.90  
  Purchase #7 $69.36   6.519%   $73.8816   $73.88   $73.90   $73.90  
  7 purchase totals = $945.22       $1,011.7518   $1,011.75   $1,011.80   $1,011.70