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 $186.91   11.558%   $208.5131   $208.51   $208.50   $208.50  
  Purchase #2 $37.62   4.226%   $39.2098   $39.21   $39.20   $39.20  
  Purchase #3 $69.32   5.854%   $73.378   $73.38   $73.40   $73.40  
  Purchase #4 $226.74   11.584%   $253.0056   $253.01   $253.00   $253.00  
  Purchase #5 $201.97   8.853%   $219.8504   $219.85   $219.85   $219.90  
  Purchase #6 $89.90   10.386%   $99.237   $99.24   $99.25   $99.20  
  Purchase #7 $126.62   3.420%   $130.9504   $130.95   $130.95   $131.00  
  7 purchase totals = $939.08       $1,024.1443   $1,024.15   $1,024.15   $1,024.20