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 $201.32   12.264%   $226.0099   $226.01   $226.00   $226.00  
  Purchase #2 $126.81   12.407%   $142.5433   $142.54   $142.55   $142.50  
  Purchase #3 $21.70   6.530%   $23.117   $23.12   $23.10   $23.10  
  Purchase #4 $236.66   5.673%   $250.0857   $250.09   $250.10   $250.10  
  Purchase #5 $68.46   11.333%   $76.2186   $76.22   $76.20   $76.20  
  Purchase #6 $62.48   13.242%   $70.7536   $70.75   $70.75   $70.80  
  Purchase #7 $220.28   6.292%   $234.14   $234.14   $234.15   $234.10  
  7 purchase totals = $937.71       $1,022.8681   $1,022.87   $1,022.85   $1,022.80