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 $41.43   13.393%   $46.9787   $46.98   $47.00   $47.00  
  Purchase #2 $119.67   12.506%   $134.6359   $134.64   $134.65   $134.60  
  Purchase #3 $235.33   12.853%   $265.577   $265.58   $265.60   $265.60  
  Purchase #4 $135.65   5.724%   $143.4146   $143.41   $143.40   $143.40  
  Purchase #5 $37.88   3.391%   $39.1645   $39.16   $39.15   $39.20  
  Purchase #6 $12.26   4.140%   $12.7676   $12.77   $12.75   $12.80  
  Purchase #7 $114.77   7.791%   $123.7117   $123.71   $123.70   $123.70  
  7 purchase totals = $696.99       $766.2500   $766.25   $766.25   $766.30