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 $247.78   6.113%   $262.9268   $262.93   $262.95   $262.90  
  Purchase #2 $128.46   10.161%   $141.5128   $141.51   $141.50   $141.50  
  Purchase #3 $249.96   6.267%   $265.625   $265.63   $265.65   $265.60  
  Purchase #4 $15.84   11.610%   $17.679   $17.68   $17.70   $17.70  
  Purchase #5 $124.84   6.721%   $133.2305   $133.23   $133.25   $133.20  
  Purchase #6 $184.37   11.416%   $205.4177   $205.42   $205.40   $205.40  
  Purchase #7 $160.44   12.782%   $180.9474   $180.95   $180.95   $180.90  
  7 purchase totals = $1,111.69       $1,207.3392   $1,207.35   $1,207.40   $1,207.20