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 $54.83   3.623%   $56.8165   $56.82   $56.80   $56.80  
  Purchase #2 $132.44   8.388%   $143.5491   $143.55   $143.55   $143.50  
  Purchase #3 $217.86   9.102%   $237.6896   $237.69   $237.70   $237.70  
  Purchase #4 $127.64   5.499%   $134.6589   $134.66   $134.65   $134.70  
  Purchase #5 $161.40   5.275%   $169.9139   $169.91   $169.90   $169.90  
  Purchase #6 $10.97   6.551%   $11.6886   $11.69   $11.70   $11.70  
  Purchase #7 $200.76   12.725%   $226.3067   $226.31   $226.30   $226.30  
  7 purchase totals = $905.90       $980.6233   $980.63   $980.60   $980.60