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 $126.51   10.337%   $139.5873   $139.59   $139.60   $139.60  
  Purchase #2 $39.88   11.726%   $44.5563   $44.56   $44.55   $44.60  
  Purchase #3 $250.93   12.335%   $281.8822   $281.88   $281.90   $281.90  
  Purchase #4 $56.61   6.202%   $60.121   $60.12   $60.10   $60.10  
  Purchase #5 $216.61   11.381%   $241.2624   $241.26   $241.25   $241.30  
  Purchase #6 $106.36   6.725%   $113.5127   $113.51   $113.50   $113.50  
  Purchase #7 $119.50   8.192%   $129.2894   $129.29   $129.30   $129.30  
  7 purchase totals = $916.40       $1,010.2113   $1,010.21   $1,010.20   $1,010.30