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 $61.69   11.680%   $68.8954   $68.90   $68.90   $68.90  
  Purchase #2 $174.60   10.553%   $193.0255   $193.03   $193.05   $193.00  
  Purchase #3 $245.84   6.167%   $261.001   $261.00   $261.00   $261.00  
  Purchase #4 $46.54   12.840%   $52.5157   $52.52   $52.50   $52.50  
  Purchase #5 $42.87   8.747%   $46.6198   $46.62   $46.60   $46.60  
  Purchase #6 $5.28   7.654%   $5.6841   $5.68   $5.70   $5.70  
  Purchase #7 $87.66   3.313%   $90.5642   $90.56   $90.55   $90.60  
  7 purchase totals = $664.48       $718.3057   $718.31   $718.30   $718.30