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 $246.70   6.143%   $261.8548   $261.85   $261.85   $261.90  
  Purchase #2 $115.80   5.306%   $121.9443   $121.94   $121.95   $121.90  
  Purchase #3 $184.65   7.360%   $198.2402   $198.24   $198.25   $198.20  
  Purchase #4 $105.92   4.828%   $111.0338   $111.03   $111.05   $111.00  
  Purchase #5 $16.78   4.832%   $17.5908   $17.59   $17.60   $17.60  
  Purchase #6 $124.83   5.594%   $131.813   $131.81   $131.80   $131.80  
  Purchase #7 $112.85   3.252%   $116.5199   $116.52   $116.50   $116.50  
  7 purchase totals = $907.53       $958.9968   $958.98   $959.00   $958.90