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 $114.83   11.792%   $128.3708   $128.37   $128.35   $128.40  
  Purchase #2 $168.38   8.467%   $182.6367   $182.64   $182.65   $182.60  
  Purchase #3 $130.59   4.679%   $136.7003   $136.70   $136.70   $136.70  
  Purchase #4 $103.91   13.568%   $118.0085   $118.01   $118.00   $118.00  
  Purchase #5 $111.44   3.364%   $115.1888   $115.19   $115.20   $115.20  
  Purchase #6 $69.87   8.647%   $75.9117   $75.91   $75.90   $75.90  
  Purchase #7 $249.34   7.680%   $268.4893   $268.49   $268.50   $268.50  
  7 purchase totals = $948.36       $1,025.3061   $1,025.31   $1,025.30   $1,025.30