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 $97.58   8.858%   $106.2236   $106.22   $106.20   $106.20  
  Purchase #2 $175.44   6.306%   $186.5032   $186.50   $186.50   $186.50  
  Purchase #3 $50.87   12.477%   $57.217   $57.22   $57.20   $57.20  
  Purchase #4 $172.92   4.189%   $180.1636   $180.16   $180.15   $180.20  
  Purchase #5 $212.69   7.715%   $229.099   $229.10   $229.10   $229.10  
  Purchase #6 $5.47   6.271%   $5.813   $5.81   $5.80   $5.80  
  Purchase #7 $71.51   7.546%   $76.9061   $76.91   $76.90   $76.90  
  7 purchase totals = $786.48       $841.9255   $841.92   $841.85   $841.90