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 $239.50   10.650%   $265.0068   $265.01   $265.00   $265.00  
  Purchase #2 $93.54   4.239%   $97.5052   $97.51   $97.50   $97.50  
  Purchase #3 $37.31   11.327%   $41.5361   $41.54   $41.55   $41.50  
  Purchase #4 $226.75   7.134%   $242.9263   $242.93   $242.95   $242.90  
  Purchase #5 $204.61   5.225%   $215.3009   $215.30   $215.30   $215.30  
  Purchase #6 $220.58   4.299%   $230.0627   $230.06   $230.05   $230.10  
  Purchase #7 $71.38   5.548%   $75.3402   $75.34   $75.35   $75.30  
  7 purchase totals = $1,093.67       $1,167.6782   $1,167.69   $1,167.70   $1,167.60