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 $249.42   8.634%   $270.9549   $270.95   $270.95   $271.00  
  Purchase #2 $119.54   10.165%   $131.6912   $131.69   $131.70   $131.70  
  Purchase #3 $55.36   8.642%   $60.1442   $60.14   $60.15   $60.10  
  Purchase #4 $127.36   5.674%   $134.5864   $134.59   $134.60   $134.60  
  Purchase #5 $106.43   9.430%   $116.4663   $116.47   $116.45   $116.50  
  Purchase #6 $198.70   11.541%   $221.632   $221.63   $221.65   $221.60  
  Purchase #7 $102.80   10.122%   $113.2054   $113.21   $113.20   $113.20  
  7 purchase totals = $959.61       $1,048.6804   $1,048.68   $1,048.70   $1,048.70