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 $191.73   7.544%   $206.1941   $206.19   $206.20   $206.20  
  Purchase #2 $185.28   9.395%   $202.6871   $202.69   $202.70   $202.70  
  Purchase #3 $106.62   7.842%   $114.9811   $114.98   $115.00   $115.00  
  Purchase #4 $245.52   3.238%   $253.4699   $253.47   $253.45   $253.50  
  Purchase #5 $70.30   12.246%   $78.9089   $78.91   $78.90   $78.90  
  Purchase #6 $111.34   11.636%   $124.2955   $124.30   $124.30   $124.30  
  Purchase #7 $249.39   8.139%   $269.6879   $269.69   $269.70   $269.70  
  7 purchase totals = $1,160.18       $1,250.2245   $1,250.23   $1,250.25   $1,250.30