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 $211.32   13.216%   $239.2481   $239.25   $239.25   $239.20  
  Purchase #2 $89.81   9.383%   $98.2369   $98.24   $98.25   $98.20  
  Purchase #3 $137.65   11.137%   $152.9801   $152.98   $153.00   $153.00  
  Purchase #4 $222.41   9.493%   $243.5234   $243.52   $243.50   $243.50  
  Purchase #5 $53.37   12.609%   $60.0994   $60.10   $60.10   $60.10  
  Purchase #6 $176.25   4.107%   $183.4886   $183.49   $183.50   $183.50  
  Purchase #7 $164.60   4.167%   $171.4589   $171.46   $171.45   $171.50  
  7 purchase totals = $1,055.41       $1,149.0354   $1,149.04   $1,149.05   $1,149.00