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 $216.45   9.250%   $236.4716   $236.47   $236.45   $236.50  
  Purchase #2 $98.46   7.411%   $105.7569   $105.76   $105.75   $105.80  
  Purchase #3 $66.30   3.632%   $68.708   $68.71   $68.70   $68.70  
  Purchase #4 $199.59   4.472%   $208.5157   $208.52   $208.50   $208.50  
  Purchase #5 $31.61   7.655%   $34.0297   $34.03   $34.05   $34.00  
  Purchase #6 $95.37   11.177%   $106.0295   $106.03   $106.05   $106.00  
  Purchase #7 $93.55   3.759%   $97.0665   $97.07   $97.05   $97.10  
  7 purchase totals = $801.33       $856.5779   $856.59   $856.55   $856.60