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 $208.81   12.604%   $235.1284   $235.13   $235.15   $235.10  
  Purchase #2 $137.49   13.613%   $156.2065   $156.21   $156.20   $156.20  
  Purchase #3 $149.61   13.469%   $169.761   $169.76   $169.75   $169.80  
  Purchase #4 $215.77   11.737%   $241.0949   $241.09   $241.10   $241.10  
  Purchase #5 $246.75   9.265%   $269.6114   $269.61   $269.60   $269.60  
  Purchase #6 $236.66   13.524%   $268.6659   $268.67   $268.65   $268.70  
  Purchase #7 $105.35   4.247%   $109.8242   $109.82   $109.80   $109.80  
  7 purchase totals = $1,300.44       $1,450.2923   $1,450.29   $1,450.25   $1,450.30