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 $60.97   8.212%   $65.9769   $65.98   $66.00   $66.00  
  Purchase #2 $106.66   11.247%   $118.6561   $118.66   $118.65   $118.70  
  Purchase #3 $114.66   6.394%   $121.9914   $121.99   $122.00   $122.00  
  Purchase #4 $160.85   8.526%   $174.5641   $174.56   $174.55   $174.60  
  Purchase #5 $214.63   8.750%   $233.4101   $233.41   $233.40   $233.40  
  Purchase #6 $220.28   4.608%   $230.4305   $230.43   $230.45   $230.40  
  Purchase #7 $58.60   4.451%   $61.2083   $61.21   $61.20   $61.20  
  7 purchase totals = $936.65       $1,006.2374   $1,006.24   $1,006.25   $1,006.30