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 $188.66   12.851%   $212.9047   $212.90   $212.90   $212.90  
  Purchase #2 $244.91   6.595%   $261.0618   $261.06   $261.05   $261.10  
  Purchase #3 $145.26   8.318%   $157.3427   $157.34   $157.35   $157.30  
  Purchase #4 $66.92   3.554%   $69.2983   $69.30   $69.30   $69.30  
  Purchase #5 $221.84   9.715%   $243.3918   $243.39   $243.40   $243.40  
  Purchase #6 $225.91   8.565%   $245.2592   $245.26   $245.25   $245.30  
  Purchase #7 $69.48   10.813%   $76.9929   $76.99   $77.00   $77.00  
  7 purchase totals = $1,162.98       $1,266.2514   $1,266.24   $1,266.25   $1,266.30