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 $48.59   13.437%   $55.119   $55.12   $55.10   $55.10  
  Purchase #2 $171.88   12.114%   $192.7015   $192.70   $192.70   $192.70  
  Purchase #3 $152.71   5.482%   $161.0816   $161.08   $161.10   $161.10  
  Purchase #4 $148.27   4.213%   $154.5166   $154.52   $154.50   $154.50  
  Purchase #5 $21.30   3.831%   $22.116   $22.12   $22.10   $22.10  
  Purchase #6 $68.45   13.114%   $77.4265   $77.43   $77.45   $77.40  
  Purchase #7 $247.87   5.358%   $261.1509   $261.15   $261.15   $261.20  
  7 purchase totals = $859.07       $924.1121   $924.12   $924.10   $924.10