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 $53.30   13.648%   $60.5744   $60.57   $60.55   $60.60  
  Purchase #2 $249.69   9.590%   $273.6353   $273.64   $273.65   $273.60  
  Purchase #3 $52.34   12.180%   $58.715   $58.72   $58.70   $58.70  
  Purchase #4 $156.71   11.430%   $174.622   $174.62   $174.60   $174.60  
  Purchase #5 $174.80   8.796%   $190.1754   $190.18   $190.20   $190.20  
  Purchase #6 $246.43   11.724%   $275.3215   $275.32   $275.30   $275.30  
  Purchase #7 $248.64   8.357%   $269.4188   $269.42   $269.40   $269.40  
  7 purchase totals = $1,181.91       $1,302.4624   $1,302.47   $1,302.40   $1,302.40