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 $183.26   4.812%   $192.0785   $192.08   $192.10   $192.10  
  Purchase #2 $226.61   11.631%   $252.967   $252.97   $252.95   $253.00  
  Purchase #3 $77.43   4.197%   $80.6797   $80.68   $80.70   $80.70  
  Purchase #4 $239.99   13.251%   $271.7911   $271.79   $271.80   $271.80  
  Purchase #5 $215.81   8.499%   $234.1517   $234.15   $234.15   $234.20  
  Purchase #6 $72.61   12.687%   $81.822   $81.82   $81.80   $81.80  
  Purchase #7 $123.76   10.303%   $136.511   $136.51   $136.50   $136.50  
  7 purchase totals = $1,139.47       $1,250.0010   $1,250.00   $1,250.00   $1,250.10