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 $24.36   4.802%   $25.5298   $25.53   $25.55   $25.50  
  Purchase #2 $151.54   6.264%   $161.0325   $161.03   $161.05   $161.00  
  Purchase #3 $44.48   10.169%   $49.0032   $49.00   $49.00   $49.00  
  Purchase #4 $196.36   6.492%   $209.1077   $209.11   $209.10   $209.10  
  Purchase #5 $141.74   8.662%   $154.0175   $154.02   $154.00   $154.00  
  Purchase #6 $92.53   13.817%   $105.3149   $105.31   $105.30   $105.30  
  Purchase #7 $127.59   7.583%   $137.2651   $137.27   $137.25   $137.30  
  7 purchase totals = $778.60       $841.2707   $841.27   $841.25   $841.20