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 $201.94   6.298%   $214.6582   $214.66   $214.65   $214.70  
  Purchase #2 $49.29   10.866%   $54.6459   $54.65   $54.65   $54.60  
  Purchase #3 $30.88   11.386%   $34.396   $34.40   $34.40   $34.40  
  Purchase #4 $123.67   11.473%   $137.8587   $137.86   $137.85   $137.90  
  Purchase #5 $110.76   12.796%   $124.9328   $124.93   $124.95   $124.90  
  Purchase #6 $164.72   6.220%   $174.9656   $174.97   $174.95   $175.00  
  Purchase #7 $239.40   7.741%   $257.932   $257.93   $257.95   $257.90  
  7 purchase totals = $920.66       $999.3892   $999.40   $999.40   $999.40