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 $201.49   3.196%   $207.9296   $207.93   $207.95   $207.90  
  Purchase #2 $152.96   10.833%   $169.5302   $169.53   $169.55   $169.50  
  Purchase #3 $90.80   10.447%   $100.2859   $100.29   $100.30   $100.30  
  Purchase #4 $233.62   11.119%   $259.5962   $259.60   $259.60   $259.60  
  Purchase #5 $230.53   4.105%   $239.9933   $239.99   $240.00   $240.00  
  Purchase #6 $176.34   9.111%   $192.4063   $192.41   $192.40   $192.40  
  Purchase #7 $223.83   4.665%   $234.2717   $234.27   $234.25   $234.30  
  7 purchase totals = $1,309.57       $1,404.0132   $1,404.02   $1,404.05   $1,404.00