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 $223.76   5.340%   $235.7088   $235.71   $235.70   $235.70  
  Purchase #2 $24.83   8.409%   $26.918   $26.92   $26.90   $26.90  
  Purchase #3 $56.31   13.194%   $63.7395   $63.74   $63.75   $63.70  
  Purchase #4 $21.33   3.657%   $22.11   $22.11   $22.10   $22.10  
  Purchase #5 $90.80   8.172%   $98.2202   $98.22   $98.20   $98.20  
  Purchase #6 $168.99   9.638%   $185.2773   $185.28   $185.30   $185.30  
  Purchase #7 $41.71   6.218%   $44.3035   $44.30   $44.30   $44.30  
  7 purchase totals = $627.73       $676.2773   $676.28   $676.25   $676.20