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 $193.88   6.552%   $206.583   $206.58   $206.60   $206.60  
  Purchase #2 $105.36   6.335%   $112.0346   $112.03   $112.05   $112.00  
  Purchase #3 $12.25   6.825%   $13.0861   $13.09   $13.10   $13.10  
  Purchase #4 $177.49   11.805%   $198.4427   $198.44   $198.45   $198.40  
  Purchase #5 $149.50   9.816%   $164.1749   $164.17   $164.15   $164.20  
  Purchase #6 $65.48   4.353%   $68.3303   $68.33   $68.35   $68.30  
  Purchase #7 $245.27   3.849%   $254.7104   $254.71   $254.70   $254.70  
  7 purchase totals = $949.23       $1,017.3620   $1,017.35   $1,017.40   $1,017.30