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 $23.95   12.808%   $27.0175   $27.02   $27.00   $27.00  
  Purchase #2 $141.88   11.304%   $157.9181   $157.92   $157.90   $157.90  
  Purchase #3 $230.64   7.720%   $248.4454   $248.45   $248.45   $248.40  
  Purchase #4 $208.30   9.660%   $228.4218   $228.42   $228.40   $228.40  
  Purchase #5 $213.32   12.826%   $240.6804   $240.68   $240.70   $240.70  
  Purchase #6 $86.35   5.641%   $91.221   $91.22   $91.20   $91.20  
  Purchase #7 $241.47   4.691%   $252.7974   $252.80   $252.80   $252.80  
  7 purchase totals = $1,145.91       $1,246.5016   $1,246.51   $1,246.45   $1,246.40