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 $214.52   9.269%   $234.4039   $234.40   $234.40   $234.40  
  Purchase #2 $213.94   11.765%   $239.11   $239.11   $239.10   $239.10  
  Purchase #3 $127.64   7.231%   $136.8696   $136.87   $136.85   $136.90  
  Purchase #4 $23.61   11.424%   $26.3072   $26.31   $26.30   $26.30  
  Purchase #5 $224.52   4.184%   $233.9139   $233.91   $233.90   $233.90  
  Purchase #6 $68.46   12.456%   $76.9874   $76.99   $77.00   $77.00  
  Purchase #7 $111.25   9.870%   $122.2304   $122.23   $122.25   $122.20  
  7 purchase totals = $983.94       $1,069.8224   $1,069.82   $1,069.80   $1,069.80