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 $198.46   13.241%   $224.7381   $224.74   $224.75   $224.70  
  Purchase #2 $72.42   7.615%   $77.9348   $77.93   $77.95   $77.90  
  Purchase #3 $9.27   11.728%   $10.3572   $10.36   $10.35   $10.40  
  Purchase #4 $176.89   4.542%   $184.9243   $184.92   $184.90   $184.90  
  Purchase #5 $106.38   8.565%   $115.4914   $115.49   $115.50   $115.50  
  Purchase #6 $235.95   13.524%   $267.8599   $267.86   $267.85   $267.90  
  Purchase #7 $152.95   5.721%   $161.7003   $161.70   $161.70   $161.70  
  7 purchase totals = $952.32       $1,043.0060   $1,043.00   $1,043.00   $1,043.00