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 $199.76   11.466%   $222.6645   $222.66   $222.65   $222.70  
  Purchase #2 $12.95   10.599%   $14.3226   $14.32   $14.30   $14.30  
  Purchase #3 $209.74   7.128%   $224.6903   $224.69   $224.70   $224.70  
  Purchase #4 $92.57   5.455%   $97.6197   $97.62   $97.60   $97.60  
  Purchase #5 $222.76   12.410%   $250.4045   $250.40   $250.40   $250.40  
  Purchase #6 $246.70   8.244%   $267.0379   $267.04   $267.05   $267.00  
  Purchase #7 $6.56   10.628%   $7.2572   $7.26   $7.25   $7.30  
  7 purchase totals = $991.04       $1,083.9967   $1,083.99   $1,083.95   $1,084.00