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 $57.99   3.398%   $59.9605   $59.96   $59.95   $60.00  
  Purchase #2 $226.73   9.366%   $247.9655   $247.97   $247.95   $248.00  
  Purchase #3 $8.65   11.688%   $9.661   $9.66   $9.65   $9.70  
  Purchase #4 $111.62   6.479%   $118.8519   $118.85   $118.85   $118.90  
  Purchase #5 $175.40   9.175%   $191.493   $191.49   $191.50   $191.50  
  Purchase #6 $134.49   8.561%   $146.0037   $146.00   $146.00   $146.00  
  Purchase #7 $236.90   6.479%   $252.2488   $252.25   $252.25   $252.20  
  7 purchase totals = $951.78       $1,026.1844   $1,026.18   $1,026.15   $1,026.30