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 $186.41   6.594%   $198.7019   $198.70   $198.70   $198.70  
  Purchase #2 $98.38   11.558%   $109.7508   $109.75   $109.75   $109.80  
  Purchase #3 $10.64   6.214%   $11.3012   $11.30   $11.30   $11.30  
  Purchase #4 $139.78   12.514%   $157.2721   $157.27   $157.25   $157.30  
  Purchase #5 $232.68   4.862%   $243.9929   $243.99   $244.00   $244.00  
  Purchase #6 $38.71   9.221%   $42.2794   $42.28   $42.30   $42.30  
  Purchase #7 $218.86   13.389%   $248.1632   $248.16   $248.15   $248.20  
  7 purchase totals = $925.46       $1,011.4615   $1,011.45   $1,011.45   $1,011.60