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 $53.92   12.603%   $60.7155   $60.72   $60.70   $60.70  
  Purchase #2 $184.89   4.437%   $193.0936   $193.09   $193.10   $193.10  
  Purchase #3 $25.39   8.387%   $27.5195   $27.52   $27.50   $27.50  
  Purchase #4 $136.92   12.613%   $154.1897   $154.19   $154.20   $154.20  
  Purchase #5 $71.38   7.232%   $76.5422   $76.54   $76.55   $76.50  
  Purchase #6 $5.81   11.246%   $6.4634   $6.46   $6.45   $6.50  
  Purchase #7 $214.25   9.699%   $235.0301   $235.03   $235.05   $235.00  
  7 purchase totals = $692.56       $753.5540   $753.55   $753.55   $753.50