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 $108.58   9.640%   $119.0471   $119.05   $119.05   $119.00  
  Purchase #2 $92.66   6.206%   $98.4105   $98.41   $98.40   $98.40  
  Purchase #3 $123.49   3.291%   $127.5541   $127.55   $127.55   $127.60  
  Purchase #4 $126.51   4.861%   $132.6597   $132.66   $132.65   $132.70  
  Purchase #5 $137.62   10.838%   $152.5353   $152.54   $152.55   $152.50  
  Purchase #6 $49.99   6.124%   $53.0514   $53.05   $53.05   $53.10  
  Purchase #7 $114.30   13.539%   $129.7751   $129.78   $129.80   $129.80  
  7 purchase totals = $753.15       $813.0332   $813.04   $813.05   $813.10