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 $76.73   12.813%   $86.5614   $86.56   $86.55   $86.60  
  Purchase #2 $98.60   8.755%   $107.2324   $107.23   $107.25   $107.20  
  Purchase #3 $78.70   7.107%   $84.2932   $84.29   $84.30   $84.30  
  Purchase #4 $228.56   3.721%   $237.0647   $237.06   $237.05   $237.10  
  Purchase #5 $187.61   11.713%   $209.5848   $209.58   $209.60   $209.60  
  Purchase #6 $155.31   13.786%   $176.721   $176.72   $176.70   $176.70  
  Purchase #7 $142.61   3.412%   $147.4759   $147.48   $147.50   $147.50  
  7 purchase totals = $968.12       $1,048.9334   $1,048.92   $1,048.95   $1,049.00