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 $236.87   10.146%   $260.9028   $260.90   $260.90   $260.90  
  Purchase #2 $199.93   10.519%   $220.9606   $220.96   $220.95   $221.00  
  Purchase #3 $234.81   10.573%   $259.6365   $259.64   $259.65   $259.60  
  Purchase #4 $244.87   9.216%   $267.4372   $267.44   $267.45   $267.40  
  Purchase #5 $239.97   4.489%   $250.7423   $250.74   $250.75   $250.70  
  Purchase #6 $123.76   8.411%   $134.1695   $134.17   $134.15   $134.20  
  Purchase #7 $46.71   7.136%   $50.0432   $50.04   $50.05   $50.00  
  7 purchase totals = $1,326.92       $1,443.8921   $1,443.89   $1,443.90   $1,443.80