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 $125.95   12.457%   $141.6396   $141.64   $141.65   $141.60  
  Purchase #2 $75.88   5.197%   $79.8235   $79.82   $79.80   $79.80  
  Purchase #3 $158.95   13.675%   $180.6864   $180.69   $180.70   $180.70  
  Purchase #4 $43.80   7.357%   $47.0224   $47.02   $47.00   $47.00  
  Purchase #5 $76.36   11.358%   $85.033   $85.03   $85.05   $85.00  
  Purchase #6 $104.80   8.687%   $113.904   $113.90   $113.90   $113.90  
  Purchase #7 $220.64   13.345%   $250.0844   $250.08   $250.10   $250.10  
  7 purchase totals = $806.38       $898.1933   $898.18   $898.20   $898.10