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 $208.61   13.132%   $236.0047   $236.00   $236.00   $236.00  
  Purchase #2 $228.26   11.690%   $254.9436   $254.94   $254.95   $254.90  
  Purchase #3 $92.98   9.301%   $101.6281   $101.63   $101.65   $101.60  
  Purchase #4 $10.55   4.769%   $11.0531   $11.05   $11.05   $11.10  
  Purchase #5 $95.70   12.559%   $107.719   $107.72   $107.70   $107.70  
  Purchase #6 $188.48   3.357%   $194.8073   $194.81   $194.80   $194.80  
  Purchase #7 $243.76   12.347%   $273.857   $273.86   $273.85   $273.90  
  7 purchase totals = $1,068.34       $1,180.0128   $1,180.01   $1,180.00   $1,180.00