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 $106.69   8.423%   $115.6765   $115.68   $115.70   $115.70  
  Purchase #2 $97.66   13.202%   $110.5531   $110.55   $110.55   $110.60  
  Purchase #3 $122.27   7.444%   $131.3718   $131.37   $131.35   $131.40  
  Purchase #4 $151.35   4.374%   $157.97   $157.97   $157.95   $158.00  
  Purchase #5 $77.88   4.249%   $81.1891   $81.19   $81.20   $81.20  
  Purchase #6 $46.59   10.119%   $51.3044   $51.30   $51.30   $51.30  
  Purchase #7 $23.56   11.213%   $26.2018   $26.20   $26.20   $26.20  
  7 purchase totals = $626.00       $674.2667   $674.26   $674.25   $674.40