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 $237.53   8.509%   $257.7414   $257.74   $257.75   $257.70  
  Purchase #2 $150.92   8.710%   $164.0651   $164.07   $164.05   $164.10  
  Purchase #3 $70.25   8.539%   $76.2486   $76.25   $76.25   $76.20  
  Purchase #4 $23.56   12.564%   $26.5201   $26.52   $26.50   $26.50  
  Purchase #5 $208.26   8.635%   $226.2433   $226.24   $226.25   $226.20  
  Purchase #6 $239.36   3.520%   $247.7855   $247.79   $247.80   $247.80  
  Purchase #7 $202.35   4.469%   $211.393   $211.39   $211.40   $211.40  
  7 purchase totals = $1,132.23       $1,209.9970   $1,210.00   $1,210.00   $1,209.90