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 $126.26   11.338%   $140.5754   $140.58   $140.60   $140.60  
  Purchase #2 $53.85   3.389%   $55.675   $55.68   $55.70   $55.70  
  Purchase #3 $48.65   9.242%   $53.1462   $53.15   $53.15   $53.10  
  Purchase #4 $47.40   6.494%   $50.4782   $50.48   $50.50   $50.50  
  Purchase #5 $211.68   9.352%   $231.4763   $231.48   $231.50   $231.50  
  Purchase #6 $129.75   13.114%   $146.7654   $146.77   $146.75   $146.80  
  Purchase #7 $139.62   3.397%   $144.3629   $144.36   $144.35   $144.40  
  7 purchase totals = $757.21       $822.4794   $822.50   $822.55   $822.60