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 $56.76   10.867%   $62.9281   $62.93   $62.95   $62.90  
  Purchase #2 $220.30   4.524%   $230.2664   $230.27   $230.25   $230.30  
  Purchase #3 $51.61   7.325%   $55.3904   $55.39   $55.40   $55.40  
  Purchase #4 $190.55   6.776%   $203.4617   $203.46   $203.45   $203.50  
  Purchase #5 $130.51   11.249%   $145.1911   $145.19   $145.20   $145.20  
  Purchase #6 $107.37   7.611%   $115.5419   $115.54   $115.55   $115.50  
  Purchase #7 $158.97   9.864%   $174.6508   $174.65   $174.65   $174.70  
  7 purchase totals = $916.07       $987.4304   $987.43   $987.45   $987.50