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 $61.31   11.834%   $68.5654   $68.57   $68.55   $68.60  
  Purchase #2 $208.40   13.362%   $236.2464   $236.25   $236.25   $236.20  
  Purchase #3 $149.59   4.204%   $155.8788   $155.88   $155.90   $155.90  
  Purchase #4 $119.49   10.227%   $131.7102   $131.71   $131.70   $131.70  
  Purchase #5 $37.69   6.757%   $40.2367   $40.24   $40.25   $40.20  
  Purchase #6 $234.44   11.102%   $260.4675   $260.47   $260.45   $260.50  
  Purchase #7 $7.71   11.255%   $8.5778   $8.58   $8.60   $8.60  
  7 purchase totals = $818.63       $901.6828   $901.70   $901.70   $901.70