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 $202.83   4.835%   $212.6368   $212.64   $212.65   $212.60  
  Purchase #2 $73.95   7.574%   $79.551   $79.55   $79.55   $79.60  
  Purchase #3 $60.72   10.821%   $67.2905   $67.29   $67.30   $67.30  
  Purchase #4 $153.36   10.641%   $169.679   $169.68   $169.70   $169.70  
  Purchase #5 $71.30   6.724%   $76.0942   $76.09   $76.10   $76.10  
  Purchase #6 $6.78   12.511%   $7.6282   $7.63   $7.65   $7.60  
  Purchase #7 $167.38   13.348%   $189.7219   $189.72   $189.70   $189.70  
  7 purchase totals = $736.32       $802.6016   $802.60   $802.65   $802.60