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 $111.95   6.590%   $119.3275   $119.33   $119.35   $119.30  
  Purchase #2 $162.94   8.258%   $176.3956   $176.40   $176.40   $176.40  
  Purchase #3 $122.26   11.311%   $136.0888   $136.09   $136.10   $136.10  
  Purchase #4 $84.82   12.445%   $95.3758   $95.38   $95.40   $95.40  
  Purchase #5 $250.96   10.311%   $276.8365   $276.84   $276.85   $276.80  
  Purchase #6 $45.41   8.242%   $49.1527   $49.15   $49.15   $49.20  
  Purchase #7 $205.72   9.321%   $224.8952   $224.90   $224.90   $224.90  
  7 purchase totals = $984.06       $1,078.0721   $1,078.09   $1,078.15   $1,078.10