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 $185.36   11.353%   $206.4039   $206.40   $206.40   $206.40  
  Purchase #2 $13.31   6.664%   $14.197   $14.20   $14.20   $14.20  
  Purchase #3 $105.67   8.444%   $114.5928   $114.59   $114.60   $114.60  
  Purchase #4 $91.71   13.107%   $103.7304   $103.73   $103.75   $103.70  
  Purchase #5 $195.63   5.446%   $206.284   $206.28   $206.30   $206.30  
  Purchase #6 $182.36   13.815%   $207.553   $207.55   $207.55   $207.60  
  Purchase #7 $139.48   5.806%   $147.5782   $147.58   $147.60   $147.60  
  7 purchase totals = $913.52       $1,000.3393   $1,000.33   $1,000.40   $1,000.40