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 $206.35   12.692%   $232.5399   $232.54   $232.55   $232.50  
  Purchase #2 $156.95   12.106%   $175.9504   $175.95   $175.95   $176.00  
  Purchase #3 $165.71   12.580%   $186.5563   $186.56   $186.55   $186.60  
  Purchase #4 $231.49   4.693%   $242.3538   $242.35   $242.35   $242.40  
  Purchase #5 $34.99   4.147%   $36.441   $36.44   $36.45   $36.40  
  Purchase #6 $77.49   6.531%   $82.5509   $82.55   $82.55   $82.60  
  Purchase #7 $45.86   3.592%   $47.5073   $47.51   $47.50   $47.50  
  7 purchase totals = $918.84       $1,003.8996   $1,003.90   $1,003.90   $1,004.00