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 $203.60   13.552%   $231.1919   $231.19   $231.20   $231.20  
  Purchase #2 $39.86   5.493%   $42.0495   $42.05   $42.05   $42.00  
  Purchase #3 $68.93   7.407%   $74.0356   $74.04   $74.05   $74.00  
  Purchase #4 $97.91   13.622%   $111.2473   $111.25   $111.25   $111.20  
  Purchase #5 $26.84   12.554%   $30.2095   $30.21   $30.20   $30.20  
  Purchase #6 $190.31   5.570%   $200.9103   $200.91   $200.90   $200.90  
  Purchase #7 $36.55   13.543%   $41.5   $41.50   $41.50   $41.50  
  7 purchase totals = $664.00       $731.1441   $731.15   $731.15   $731.00