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 $220.68   8.731%   $239.9476   $239.95   $239.95   $239.90  
  Purchase #2 $106.56   12.526%   $119.9077   $119.91   $119.90   $119.90  
  Purchase #3 $114.27   12.212%   $128.2247   $128.22   $128.20   $128.20  
  Purchase #4 $143.38   12.474%   $161.2652   $161.27   $161.25   $161.30  
  Purchase #5 $202.89   10.796%   $224.794   $224.79   $224.80   $224.80  
  Purchase #6 $223.29   3.419%   $230.9243   $230.92   $230.90   $230.90  
  Purchase #7 $42.36   11.204%   $47.106   $47.11   $47.10   $47.10  
  7 purchase totals = $1,053.43       $1,152.1695   $1,152.17   $1,152.10   $1,152.10