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 $54.83   5.308%   $57.7404   $57.74   $57.75   $57.70  
  Purchase #2 $217.82   6.351%   $231.6537   $231.65   $231.65   $231.70  
  Purchase #3 $225.91   3.384%   $233.5548   $233.55   $233.55   $233.60  
  Purchase #4 $14.54   3.512%   $15.0506   $15.05   $15.05   $15.10  
  Purchase #5 $182.46   12.657%   $205.554   $205.55   $205.55   $205.60  
  Purchase #6 $182.88   13.792%   $208.1028   $208.10   $208.10   $208.10  
  Purchase #7 $231.59   9.476%   $253.5355   $253.54   $253.55   $253.50  
  7 purchase totals = $1,110.03       $1,205.1918   $1,205.18   $1,205.20   $1,205.30