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 $213.95   13.564%   $242.9702   $242.97   $242.95   $243.00  
  Purchase #2 $37.37   3.414%   $38.6458   $38.65   $38.65   $38.60  
  Purchase #3 $52.44   12.323%   $58.9022   $58.90   $58.90   $58.90  
  Purchase #4 $174.56   12.105%   $195.6905   $195.69   $195.70   $195.70  
  Purchase #5 $55.70   10.813%   $61.7228   $61.72   $61.70   $61.70  
  Purchase #6 $185.88   5.423%   $195.9603   $195.96   $195.95   $196.00  
  Purchase #7 $238.75   7.692%   $257.1147   $257.11   $257.10   $257.10  
  7 purchase totals = $958.65       $1,051.0065   $1,051.00   $1,050.95   $1,051.00