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 $49.74   11.690%   $55.5546   $55.55   $55.55   $55.60  
  Purchase #2 $196.72   4.424%   $205.4229   $205.42   $205.40   $205.40  
  Purchase #3 $115.81   7.662%   $124.6834   $124.68   $124.70   $124.70  
  Purchase #4 $71.61   7.250%   $76.8017   $76.80   $76.80   $76.80  
  Purchase #5 $205.76   8.511%   $223.2722   $223.27   $223.25   $223.30  
  Purchase #6 $51.67   5.583%   $54.5547   $54.55   $54.55   $54.60  
  Purchase #7 $25.98   5.322%   $27.3627   $27.36   $27.35   $27.40  
  7 purchase totals = $717.29       $767.6522   $767.63   $767.60   $767.80