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 $59.69   8.356%   $64.6777   $64.68   $64.70   $64.70  
  Purchase #2 $192.60   4.724%   $201.6984   $201.70   $201.70   $201.70  
  Purchase #3 $170.93   7.398%   $183.5754   $183.58   $183.60   $183.60  
  Purchase #4 $32.26   6.760%   $34.4408   $34.44   $34.45   $34.40  
  Purchase #5 $172.62   11.617%   $192.6733   $192.67   $192.65   $192.70  
  Purchase #6 $64.28   13.607%   $73.0266   $73.03   $73.05   $73.00  
  Purchase #7 $129.88   8.513%   $140.9367   $140.94   $140.95   $140.90  
  7 purchase totals = $822.26       $891.0289   $891.04   $891.10   $891.00