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 $205.63   13.777%   $233.9596   $233.96   $233.95   $234.00  
  Purchase #2 $196.66   6.628%   $209.6946   $209.69   $209.70   $209.70  
  Purchase #3 $21.25   8.397%   $23.0344   $23.03   $23.05   $23.00  
  Purchase #4 $201.94   12.111%   $226.397   $226.40   $226.40   $226.40  
  Purchase #5 $58.83   3.638%   $60.9702   $60.97   $60.95   $61.00  
  Purchase #6 $109.26   5.326%   $115.0792   $115.08   $115.10   $115.10  
  Purchase #7 $244.66   9.734%   $268.4752   $268.48   $268.50   $268.50  
  7 purchase totals = $1,038.23       $1,137.6102   $1,137.61   $1,137.65   $1,137.70