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 $207.93   13.105%   $235.1792   $235.18   $235.20   $235.20  
  Purchase #2 $141.43   7.197%   $151.6087   $151.61   $151.60   $151.60  
  Purchase #3 $60.56   8.790%   $65.8832   $65.88   $65.90   $65.90  
  Purchase #4 $129.46   9.252%   $141.4376   $141.44   $141.45   $141.40  
  Purchase #5 $134.62   5.243%   $141.6781   $141.68   $141.70   $141.70  
  Purchase #6 $89.42   9.247%   $97.6887   $97.69   $97.70   $97.70  
  Purchase #7 $55.94   6.822%   $59.7562   $59.76   $59.75   $59.80  
  7 purchase totals = $819.36       $893.2317   $893.24   $893.30   $893.30