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 $227.69   7.797%   $245.443   $245.44   $245.45   $245.40  
  Purchase #2 $245.34   13.434%   $278.299   $278.30   $278.30   $278.30  
  Purchase #3 $82.35   4.597%   $86.1356   $86.14   $86.15   $86.10  
  Purchase #4 $172.75   8.800%   $187.952   $187.95   $187.95   $188.00  
  Purchase #5 $157.69   12.621%   $177.5921   $177.59   $177.60   $177.60  
  Purchase #6 $41.56   9.481%   $45.5003   $45.50   $45.50   $45.50  
  Purchase #7 $59.36   12.869%   $66.999   $67.00   $67.00   $67.00  
  7 purchase totals = $986.74       $1,087.9210   $1,087.92   $1,087.95   $1,087.90