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 $211.97   11.511%   $236.3699   $236.37   $236.35   $236.40  
  Purchase #2 $224.60   11.426%   $250.2628   $250.26   $250.25   $250.30  
  Purchase #3 $151.69   12.526%   $170.6907   $170.69   $170.70   $170.70  
  Purchase #4 $46.36   9.138%   $50.5964   $50.60   $50.60   $50.60  
  Purchase #5 $70.25   8.354%   $76.1187   $76.12   $76.10   $76.10  
  Purchase #6 $182.64   12.281%   $205.07   $205.07   $205.05   $205.10  
  Purchase #7 $145.99   6.277%   $155.1538   $155.15   $155.15   $155.20  
  7 purchase totals = $1,033.50       $1,144.2623   $1,144.26   $1,144.20   $1,144.40