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 $225.66   10.793%   $250.0155   $250.02   $250.00   $250.00  
  Purchase #2 $128.26   10.432%   $141.6401   $141.64   $141.65   $141.60  
  Purchase #3 $123.26   5.795%   $130.4029   $130.40   $130.40   $130.40  
  Purchase #4 $26.60   13.608%   $30.2197   $30.22   $30.20   $30.20  
  Purchase #5 $167.39   8.807%   $182.132   $182.13   $182.15   $182.10  
  Purchase #6 $75.97   4.814%   $79.6272   $79.63   $79.65   $79.60  
  Purchase #7 $122.70   12.602%   $138.1627   $138.16   $138.15   $138.20  
  7 purchase totals = $869.84       $952.2001   $952.20   $952.20   $952.10