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 $196.36   11.724%   $219.3812   $219.38   $219.40   $219.40  
  Purchase #2 $60.79   4.637%   $63.6088   $63.61   $63.60   $63.60  
  Purchase #3 $159.27   4.159%   $165.894   $165.89   $165.90   $165.90  
  Purchase #4 $85.89   11.744%   $95.9769   $95.98   $96.00   $96.00  
  Purchase #5 $66.85   4.344%   $69.754   $69.75   $69.75   $69.80  
  Purchase #6 $241.53   13.553%   $274.2646   $274.26   $274.25   $274.30  
  Purchase #7 $89.58   8.436%   $97.137   $97.14   $97.15   $97.10  
  7 purchase totals = $900.27       $986.0165   $986.01   $986.05   $986.10