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 $139.68   6.128%   $148.2396   $148.24   $148.25   $148.20  
  Purchase #2 $60.66   8.191%   $65.6287   $65.63   $65.65   $65.60  
  Purchase #3 $224.79   13.437%   $254.995   $255.00   $255.00   $255.00  
  Purchase #4 $113.92   4.453%   $118.9929   $118.99   $119.00   $119.00  
  Purchase #5 $108.54   5.591%   $114.6085   $114.61   $114.60   $114.60  
  Purchase #6 $10.60   10.120%   $11.6727   $11.67   $11.65   $11.70  
  Purchase #7 $30.52   10.384%   $33.6892   $33.69   $33.70   $33.70  
  7 purchase totals = $688.71       $747.8266   $747.83   $747.85   $747.80