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 $194.97   13.662%   $221.6068   $221.61   $221.60   $221.60  
  Purchase #2 $117.58   5.547%   $124.1022   $124.10   $124.10   $124.10  
  Purchase #3 $236.90   10.757%   $262.3833   $262.38   $262.40   $262.40  
  Purchase #4 $152.31   6.515%   $162.233   $162.23   $162.25   $162.20  
  Purchase #5 $158.96   10.254%   $175.2598   $175.26   $175.25   $175.30  
  Purchase #6 $176.66   5.295%   $186.0141   $186.01   $186.00   $186.00  
  Purchase #7 $10.69   8.725%   $11.6227   $11.62   $11.60   $11.60  
  7 purchase totals = $1,048.07       $1,143.2219   $1,143.21   $1,143.20   $1,143.20