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 $68.78   10.760%   $76.1807   $76.18   $76.20   $76.20  
  Purchase #2 $105.29   9.391%   $115.1778   $115.18   $115.20   $115.20  
  Purchase #3 $185.87   12.412%   $208.9402   $208.94   $208.95   $208.90  
  Purchase #4 $250.75   7.589%   $269.7794   $269.78   $269.80   $269.80  
  Purchase #5 $114.40   13.838%   $130.2307   $130.23   $130.25   $130.20  
  Purchase #6 $216.71   11.182%   $240.9425   $240.94   $240.95   $240.90  
  Purchase #7 $11.40   3.749%   $11.8274   $11.83   $11.85   $11.80  
  7 purchase totals = $953.20       $1,053.0787   $1,053.08   $1,053.20   $1,053.00