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 $44.74   9.588%   $49.0297   $49.03   $49.05   $49.00  
  Purchase #2 $131.61   7.141%   $141.0083   $141.01   $141.00   $141.00  
  Purchase #3 $79.39   8.296%   $85.9762   $85.98   $86.00   $86.00  
  Purchase #4 $164.74   4.317%   $171.8518   $171.85   $171.85   $171.90  
  Purchase #5 $81.81   12.452%   $91.997   $92.00   $92.00   $92.00  
  Purchase #6 $250.47   12.590%   $282.0042   $282.00   $282.00   $282.00  
  Purchase #7 $183.47   8.192%   $198.4999   $198.50   $198.50   $198.50  
  7 purchase totals = $936.23       $1,020.3671   $1,020.37   $1,020.40   $1,020.40