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 $18.78   3.854%   $19.5038   $19.50   $19.50   $19.50  
  Purchase #2 $168.88   13.244%   $191.2465   $191.25   $191.25   $191.20  
  Purchase #3 $167.48   4.524%   $175.0568   $175.06   $175.05   $175.10  
  Purchase #4 $147.97   6.281%   $157.264   $157.26   $157.25   $157.30  
  Purchase #5 $14.43   6.441%   $15.3594   $15.36   $15.35   $15.40  
  Purchase #6 $132.46   6.773%   $141.4315   $141.43   $141.45   $141.40  
  Purchase #7 $213.39   6.411%   $227.0704   $227.07   $227.05   $227.10  
  7 purchase totals = $863.39       $926.9324   $926.93   $926.90   $927.00