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 $236.41   11.784%   $264.2686   $264.27   $264.25   $264.30  
  Purchase #2 $241.90   5.664%   $255.6012   $255.60   $255.60   $255.60  
  Purchase #3 $222.49   6.278%   $236.4579   $236.46   $236.45   $236.50  
  Purchase #4 $118.94   13.241%   $134.6888   $134.69   $134.70   $134.70  
  Purchase #5 $115.26   7.589%   $124.0071   $124.01   $124.00   $124.00  
  Purchase #6 $208.39   9.313%   $227.7974   $227.80   $227.80   $227.80  
  Purchase #7 $23.43   5.621%   $24.747   $24.75   $24.75   $24.70  
  7 purchase totals = $1,166.82       $1,267.5680   $1,267.58   $1,267.55   $1,267.60