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 $205.29   9.144%   $224.0617   $224.06   $224.05   $224.10  
  Purchase #2 $163.56   13.676%   $185.9285   $185.93   $185.95   $185.90  
  Purchase #3 $121.88   12.194%   $136.742   $136.74   $136.75   $136.70  
  Purchase #4 $208.36   7.135%   $223.2265   $223.23   $223.25   $223.20  
  Purchase #5 $130.61   3.515%   $135.2009   $135.20   $135.20   $135.20  
  Purchase #6 $168.54   8.538%   $182.9299   $182.93   $182.95   $182.90  
  Purchase #7 $167.94   13.836%   $191.1762   $191.18   $191.20   $191.20  
  7 purchase totals = $1,166.18       $1,279.2657   $1,279.27   $1,279.35   $1,279.20