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 $208.83   13.753%   $237.5504   $237.55   $237.55   $237.60  
  Purchase #2 $228.60   7.282%   $245.2467   $245.25   $245.25   $245.20  
  Purchase #3 $81.29   10.819%   $90.0848   $90.08   $90.10   $90.10  
  Purchase #4 $139.28   5.833%   $147.4042   $147.40   $147.40   $147.40  
  Purchase #5 $184.78   4.450%   $193.0027   $193.00   $193.00   $193.00  
  Purchase #6 $44.69   3.782%   $46.3802   $46.38   $46.40   $46.40  
  Purchase #7 $46.71   5.703%   $49.3739   $49.37   $49.35   $49.40  
  7 purchase totals = $934.18       $1,009.0429   $1,009.03   $1,009.05   $1,009.10