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 $221.67   3.183%   $228.7258   $228.73   $228.75   $228.70  
  Purchase #2 $188.83   9.281%   $206.3553   $206.36   $206.35   $206.40  
  Purchase #3 $175.65   10.663%   $194.3796   $194.38   $194.40   $194.40  
  Purchase #4 $236.97   10.367%   $261.5367   $261.54   $261.55   $261.50  
  Purchase #5 $123.40   9.724%   $135.3994   $135.40   $135.40   $135.40  
  Purchase #6 $60.92   4.657%   $63.757   $63.76   $63.75   $63.80  
  Purchase #7 $41.41   5.287%   $43.5993   $43.60   $43.60   $43.60  
  7 purchase totals = $1,048.85       $1,133.7531   $1,133.77   $1,133.80   $1,133.80