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 $122.82   3.381%   $126.9725   $126.97   $126.95   $127.00  
  Purchase #2 $220.88   6.811%   $235.9241   $235.92   $235.90   $235.90  
  Purchase #3 $68.61   8.606%   $74.5146   $74.51   $74.50   $74.50  
  Purchase #4 $190.37   3.229%   $196.517   $196.52   $196.50   $196.50  
  Purchase #5 $37.83   5.127%   $39.7695   $39.77   $39.75   $39.80  
  Purchase #6 $89.93   10.469%   $99.3448   $99.34   $99.35   $99.30  
  Purchase #7 $177.47   4.849%   $186.0755   $186.08   $186.10   $186.10  
  7 purchase totals = $907.91       $959.1180   $959.11   $959.05   $959.10