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 $246.69   9.153%   $269.2695   $269.27   $269.25   $269.30  
  Purchase #2 $65.99   13.485%   $74.8888   $74.89   $74.90   $74.90  
  Purchase #3 $156.27   13.182%   $176.8695   $176.87   $176.85   $176.90  
  Purchase #4 $227.67   5.254%   $239.6318   $239.63   $239.65   $239.60  
  Purchase #5 $175.85   5.816%   $186.0774   $186.08   $186.10   $186.10  
  Purchase #6 $172.25   12.136%   $193.1543   $193.15   $193.15   $193.20  
  Purchase #7 $52.82   8.798%   $57.4671   $57.47   $57.45   $57.50  
  7 purchase totals = $1,097.54       $1,197.3584   $1,197.36   $1,197.35   $1,197.50