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 $75.42   8.815%   $82.0683   $82.07   $82.05   $82.10  
  Purchase #2 $92.84   6.260%   $98.6518   $98.65   $98.65   $98.70  
  Purchase #3 $194.25   8.327%   $210.4252   $210.43   $210.45   $210.40  
  Purchase #4 $160.47   5.423%   $169.1723   $169.17   $169.15   $169.20  
  Purchase #5 $214.51   9.670%   $235.2531   $235.25   $235.25   $235.30  
  Purchase #6 $95.33   11.105%   $105.9164   $105.92   $105.90   $105.90  
  Purchase #7 $49.77   6.230%   $52.8707   $52.87   $52.85   $52.90  
  7 purchase totals = $882.59       $954.3578   $954.36   $954.30   $954.50