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 $59.41   12.111%   $66.6051   $66.61   $66.60   $66.60  
  Purchase #2 $152.43   3.806%   $158.2315   $158.23   $158.25   $158.20  
  Purchase #3 $52.27   10.867%   $57.9502   $57.95   $57.95   $58.00  
  Purchase #4 $185.32   11.532%   $206.6911   $206.69   $206.70   $206.70  
  Purchase #5 $184.51   4.217%   $192.2908   $192.29   $192.30   $192.30  
  Purchase #6 $125.74   8.259%   $136.1249   $136.12   $136.10   $136.10  
  Purchase #7 $59.51   4.248%   $62.038   $62.04   $62.05   $62.00  
  7 purchase totals = $819.19       $879.9316   $879.93   $879.95   $879.90