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 $14.95   8.488%   $16.219   $16.22   $16.20   $16.20  
  Purchase #2 $96.78   11.260%   $107.6774   $107.68   $107.70   $107.70  
  Purchase #3 $157.41   4.792%   $164.9531   $164.95   $164.95   $165.00  
  Purchase #4 $224.69   3.284%   $232.0688   $232.07   $232.05   $232.10  
  Purchase #5 $173.97   5.194%   $183.006   $183.01   $183.00   $183.00  
  Purchase #6 $245.42   6.772%   $262.0398   $262.04   $262.05   $262.00  
  Purchase #7 $63.84   8.732%   $69.4145   $69.41   $69.40   $69.40  
  7 purchase totals = $977.06       $1,035.3786   $1,035.38   $1,035.35   $1,035.40