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 $194.38   10.163%   $214.1348   $214.13   $214.15   $214.10  
  Purchase #2 $111.75   8.624%   $121.3873   $121.39   $121.40   $121.40  
  Purchase #3 $50.25   7.562%   $54.0499   $54.05   $54.05   $54.00  
  Purchase #4 $79.47   3.801%   $82.4907   $82.49   $82.50   $82.50  
  Purchase #5 $114.88   3.529%   $118.9341   $118.93   $118.95   $118.90  
  Purchase #6 $184.76   4.408%   $192.9042   $192.90   $192.90   $192.90  
  Purchase #7 $213.67   12.344%   $240.0454   $240.05   $240.05   $240.00  
  7 purchase totals = $949.16       $1,023.9464   $1,023.94   $1,024.00   $1,023.80