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 $218.51   11.534%   $243.7129   $243.71   $243.70   $243.70  
  Purchase #2 $160.88   10.517%   $177.7997   $177.80   $177.80   $177.80  
  Purchase #3 $144.86   11.511%   $161.5348   $161.53   $161.55   $161.50  
  Purchase #4 $119.68   4.184%   $124.6874   $124.69   $124.70   $124.70  
  Purchase #5 $102.96   11.523%   $114.8241   $114.82   $114.80   $114.80  
  Purchase #6 $126.75   8.697%   $137.7734   $137.77   $137.75   $137.80  
  Purchase #7 $106.35   7.608%   $114.4411   $114.44   $114.45   $114.40  
  7 purchase totals = $979.99       $1,074.7734   $1,074.76   $1,074.75   $1,074.70