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 $60.82   3.492%   $62.9438   $62.94   $62.95   $62.90  
  Purchase #2 $107.41   5.508%   $113.3261   $113.33   $113.35   $113.30  
  Purchase #3 $220.93   8.105%   $238.8364   $238.84   $238.85   $238.80  
  Purchase #4 $113.95   13.536%   $129.3743   $129.37   $129.35   $129.40  
  Purchase #5 $241.45   7.451%   $259.4404   $259.44   $259.45   $259.40  
  Purchase #6 $131.55   7.710%   $141.6925   $141.69   $141.70   $141.70  
  Purchase #7 $43.41   7.799%   $46.7955   $46.80   $46.80   $46.80  
  7 purchase totals = $919.52       $992.4090   $992.41   $992.45   $992.30