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 $23.76   9.797%   $26.0878   $26.09   $26.10   $26.10  
  Purchase #2 $201.58   6.788%   $215.2633   $215.26   $215.25   $215.30  
  Purchase #3 $36.36   5.793%   $38.4663   $38.47   $38.45   $38.50  
  Purchase #4 $61.56   9.551%   $67.4396   $67.44   $67.45   $67.40  
  Purchase #5 $208.86   5.178%   $219.6748   $219.67   $219.65   $219.70  
  Purchase #6 $228.42   5.327%   $240.5879   $240.59   $240.60   $240.60  
  Purchase #7 $125.31   4.242%   $130.6257   $130.63   $130.65   $130.60  
  7 purchase totals = $885.85       $938.1454   $938.15   $938.15   $938.20