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 $208.84   11.832%   $233.5499   $233.55   $233.55   $233.50  
  Purchase #2 $63.91   6.399%   $67.9996   $68.00   $68.00   $68.00  
  Purchase #3 $217.46   9.762%   $238.6884   $238.69   $238.70   $238.70  
  Purchase #4 $173.54   11.575%   $193.6273   $193.63   $193.65   $193.60  
  Purchase #5 $60.33   11.346%   $67.175   $67.18   $67.20   $67.20  
  Purchase #6 $147.82   3.834%   $153.4874   $153.49   $153.50   $153.50  
  Purchase #7 $77.62   11.157%   $86.2801   $86.28   $86.30   $86.30  
  7 purchase totals = $949.52       $1,040.8077   $1,040.82   $1,040.90   $1,040.80