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 $216.95   5.433%   $228.7369   $228.74   $228.75   $228.70  
  Purchase #2 $53.81   3.285%   $55.5777   $55.58   $55.60   $55.60  
  Purchase #3 $108.88   10.689%   $120.5182   $120.52   $120.50   $120.50  
  Purchase #4 $44.40   3.746%   $46.0632   $46.06   $46.05   $46.10  
  Purchase #5 $78.93   3.212%   $81.4652   $81.47   $81.45   $81.50  
  Purchase #6 $224.95   12.735%   $253.5974   $253.60   $253.60   $253.60  
  Purchase #7 $74.25   6.858%   $79.3421   $79.34   $79.35   $79.30  
  7 purchase totals = $802.17       $865.3007   $865.31   $865.30   $865.30