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 $160.94   10.130%   $177.2432   $177.24   $177.25   $177.20  
  Purchase #2 $216.65   10.518%   $239.4372   $239.44   $239.45   $239.40  
  Purchase #3 $99.52   8.141%   $107.6219   $107.62   $107.60   $107.60  
  Purchase #4 $184.43   12.208%   $206.9452   $206.95   $206.95   $206.90  
  Purchase #5 $48.94   13.340%   $55.4686   $55.47   $55.45   $55.50  
  Purchase #6 $41.83   10.352%   $46.1602   $46.16   $46.15   $46.20  
  Purchase #7 $126.92   5.715%   $134.1735   $134.17   $134.15   $134.20  
  7 purchase totals = $879.23       $967.0498   $967.05   $967.00   $967.00