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 $71.62   6.698%   $76.4171   $76.42   $76.40   $76.40  
  Purchase #2 $166.44   11.529%   $185.6289   $185.63   $185.65   $185.60  
  Purchase #3 $115.28   6.439%   $122.7029   $122.70   $122.70   $122.70  
  Purchase #4 $41.95   5.523%   $44.2669   $44.27   $44.25   $44.30  
  Purchase #5 $184.94   4.238%   $192.7778   $192.78   $192.80   $192.80  
  Purchase #6 $38.28   6.377%   $40.7211   $40.72   $40.70   $40.70  
  Purchase #7 $172.54   13.105%   $195.1514   $195.15   $195.15   $195.20  
  7 purchase totals = $791.05       $857.6661   $857.67   $857.65   $857.70