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 $68.38   12.353%   $76.827   $76.83   $76.85   $76.80  
  Purchase #2 $93.32   6.724%   $99.5948   $99.59   $99.60   $99.60  
  Purchase #3 $175.64   12.528%   $197.6442   $197.64   $197.65   $197.60  
  Purchase #4 $185.56   4.173%   $193.3034   $193.30   $193.30   $193.30  
  Purchase #5 $167.80   4.816%   $175.8812   $175.88   $175.90   $175.90  
  Purchase #6 $65.41   11.138%   $72.6954   $72.70   $72.70   $72.70  
  Purchase #7 $142.58   10.154%   $157.0576   $157.06   $157.05   $157.10  
  7 purchase totals = $898.69       $973.0036   $973.00   $973.05   $973.00