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 $66.61   8.153%   $72.0407   $72.04   $72.05   $72.00  
  Purchase #2 $168.42   4.122%   $175.3623   $175.36   $175.35   $175.40  
  Purchase #3 $105.49   11.169%   $117.2722   $117.27   $117.25   $117.30  
  Purchase #4 $69.27   6.175%   $73.5474   $73.55   $73.55   $73.50  
  Purchase #5 $73.90   7.347%   $79.3294   $79.33   $79.35   $79.30  
  Purchase #6 $113.27   11.405%   $126.1884   $126.19   $126.20   $126.20  
  Purchase #7 $207.35   13.235%   $234.7928   $234.79   $234.80   $234.80  
  7 purchase totals = $804.31       $878.5332   $878.53   $878.55   $878.50