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 $211.80   13.337%   $240.0478   $240.05   $240.05   $240.00  
  Purchase #2 $208.90   9.291%   $228.3089   $228.31   $228.30   $228.30  
  Purchase #3 $14.52   10.618%   $16.0617   $16.06   $16.05   $16.10  
  Purchase #4 $47.44   12.395%   $53.3202   $53.32   $53.30   $53.30  
  Purchase #5 $205.41   12.836%   $231.7764   $231.78   $231.80   $231.80  
  Purchase #6 $33.71   3.839%   $35.0041   $35.00   $35.00   $35.00  
  Purchase #7 $244.38   11.614%   $272.7623   $272.76   $272.75   $272.80  
  7 purchase totals = $966.16       $1,077.2814   $1,077.28   $1,077.25   $1,077.30