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 $86.57   11.403%   $96.4416   $96.44   $96.45   $96.40  
  Purchase #2 $151.39   8.762%   $164.6548   $164.65   $164.65   $164.70  
  Purchase #3 $16.77   8.133%   $18.1339   $18.13   $18.15   $18.10  
  Purchase #4 $239.33   6.862%   $255.7528   $255.75   $255.75   $255.80  
  Purchase #5 $113.51   4.503%   $118.6214   $118.62   $118.60   $118.60  
  Purchase #6 $135.39   5.815%   $143.2629   $143.26   $143.25   $143.30  
  Purchase #7 $69.32   4.461%   $72.4124   $72.41   $72.40   $72.40  
  7 purchase totals = $812.28       $869.2798   $869.26   $869.25   $869.30