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 $248.51   8.337%   $269.2283   $269.23   $269.25   $269.20  
  Purchase #2 $156.97   9.196%   $171.405   $171.41   $171.40   $171.40  
  Purchase #3 $69.53   9.384%   $76.0547   $76.05   $76.05   $76.10  
  Purchase #4 $51.34   6.584%   $54.7202   $54.72   $54.70   $54.70  
  Purchase #5 $239.30   12.635%   $269.5356   $269.54   $269.55   $269.50  
  Purchase #6 $209.52   13.274%   $237.3317   $237.33   $237.35   $237.30  
  Purchase #7 $174.90   5.215%   $184.021   $184.02   $184.00   $184.00  
  7 purchase totals = $1,150.07       $1,262.2965   $1,262.30   $1,262.30   $1,262.20