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 $58.47   4.801%   $61.2771   $61.28   $61.30   $61.30  
  Purchase #2 $193.80   10.400%   $213.9552   $213.96   $213.95   $214.00  
  Purchase #3 $154.54   4.755%   $161.8884   $161.89   $161.90   $161.90  
  Purchase #4 $51.90   12.216%   $58.2401   $58.24   $58.25   $58.20  
  Purchase #5 $9.37   7.225%   $10.047   $10.05   $10.05   $10.00  
  Purchase #6 $192.52   3.191%   $198.6633   $198.66   $198.65   $198.70  
  Purchase #7 $49.81   12.572%   $56.0721   $56.07   $56.05   $56.10  
  7 purchase totals = $710.41       $760.1432   $760.15   $760.15   $760.20