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 $219.51   13.785%   $249.7695   $249.77   $249.75   $249.80  
  Purchase #2 $50.45   4.271%   $52.6047   $52.60   $52.60   $52.60  
  Purchase #3 $129.69   13.591%   $147.3162   $147.32   $147.30   $147.30  
  Purchase #4 $45.86   3.436%   $47.4357   $47.44   $47.45   $47.40  
  Purchase #5 $194.58   5.730%   $205.7294   $205.73   $205.75   $205.70  
  Purchase #6 $179.96   10.147%   $198.2205   $198.22   $198.20   $198.20  
  Purchase #7 $100.81   11.274%   $112.1753   $112.18   $112.20   $112.20  
  7 purchase totals = $920.86       $1,013.2513   $1,013.26   $1,013.25   $1,013.20