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 $103.67   10.252%   $114.2982   $114.30   $114.30   $114.30  
  Purchase #2 $196.68   9.794%   $215.9428   $215.94   $215.95   $215.90  
  Purchase #3 $50.57   4.792%   $52.9933   $52.99   $53.00   $53.00  
  Purchase #4 $118.27   9.126%   $129.0633   $129.06   $129.05   $129.10  
  Purchase #5 $161.60   8.183%   $174.8237   $174.82   $174.80   $174.80  
  Purchase #6 $141.90   13.482%   $161.031   $161.03   $161.05   $161.00  
  Purchase #7 $22.32   4.670%   $23.3623   $23.36   $23.35   $23.40  
  7 purchase totals = $795.01       $871.5146   $871.50   $871.50   $871.50