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 $228.94   4.642%   $239.5674   $239.57   $239.55   $239.60  
  Purchase #2 $220.59   12.277%   $247.6718   $247.67   $247.65   $247.70  
  Purchase #3 $121.57   12.430%   $136.6812   $136.68   $136.70   $136.70  
  Purchase #4 $24.48   11.274%   $27.2399   $27.24   $27.25   $27.20  
  Purchase #5 $218.27   8.602%   $237.0456   $237.05   $237.05   $237.00  
  Purchase #6 $58.82   11.600%   $65.6431   $65.64   $65.65   $65.60  
  Purchase #7 $168.65   8.224%   $182.5198   $182.52   $182.50   $182.50  
  7 purchase totals = $1,041.32       $1,136.3688   $1,136.37   $1,136.35   $1,136.30