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 $237.93   4.447%   $248.5107   $248.51   $248.50   $248.50  
  Purchase #2 $97.87   3.766%   $101.5558   $101.56   $101.55   $101.60  
  Purchase #3 $130.25   12.597%   $146.6576   $146.66   $146.65   $146.70  
  Purchase #4 $58.73   4.687%   $61.4827   $61.48   $61.50   $61.50  
  Purchase #5 $192.76   4.285%   $201.0198   $201.02   $201.00   $201.00  
  Purchase #6 $228.64   3.430%   $236.4824   $236.48   $236.50   $236.50  
  Purchase #7 $76.64   6.142%   $81.3472   $81.35   $81.35   $81.30  
  7 purchase totals = $1,022.82       $1,077.0562   $1,077.06   $1,077.05   $1,077.10