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 $203.82   13.646%   $231.6333   $231.63   $231.65   $231.60  
  Purchase #2 $42.28   11.589%   $47.1798   $47.18   $47.20   $47.20  
  Purchase #3 $209.38   8.157%   $226.4591   $226.46   $226.45   $226.50  
  Purchase #4 $72.27   6.323%   $76.8396   $76.84   $76.85   $76.80  
  Purchase #5 $188.45   6.773%   $201.2137   $201.21   $201.20   $201.20  
  Purchase #6 $85.95   9.645%   $94.2399   $94.24   $94.25   $94.20  
  Purchase #7 $188.27   10.685%   $208.3866   $208.39   $208.40   $208.40  
  7 purchase totals = $990.42       $1,085.9520   $1,085.95   $1,086.00   $1,085.90