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 $65.92   13.694%   $74.9471   $74.95   $74.95   $74.90  
  Purchase #2 $244.70   6.211%   $259.8983   $259.90   $259.90   $259.90  
  Purchase #3 $95.55   3.282%   $98.686   $98.69   $98.70   $98.70  
  Purchase #4 $153.77   13.638%   $174.7412   $174.74   $174.75   $174.70  
  Purchase #5 $49.34   6.777%   $52.6838   $52.68   $52.70   $52.70  
  Purchase #6 $41.83   11.614%   $46.6881   $46.69   $46.70   $46.70  
  Purchase #7 $175.41   12.856%   $197.9607   $197.96   $197.95   $198.00  
  7 purchase totals = $826.52       $905.6052   $905.61   $905.65   $905.60