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 $158.63   11.291%   $176.5409   $176.54   $176.55   $176.50  
  Purchase #2 $208.97   7.679%   $225.0168   $225.02   $225.00   $225.00  
  Purchase #3 $111.25   10.299%   $122.7076   $122.71   $122.70   $122.70  
  Purchase #4 $72.91   7.119%   $78.1005   $78.10   $78.10   $78.10  
  Purchase #5 $143.66   6.469%   $152.9534   $152.95   $152.95   $153.00  
  Purchase #6 $74.51   7.584%   $80.1608   $80.16   $80.15   $80.20  
  Purchase #7 $116.60   6.769%   $124.4927   $124.49   $124.50   $124.50  
  7 purchase totals = $886.53       $959.9727   $959.97   $959.95   $960.00