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 $241.94   8.354%   $262.1517   $262.15   $262.15   $262.20  
  Purchase #2 $33.77   3.152%   $34.8344   $34.83   $34.85   $34.80  
  Purchase #3 $130.40   11.188%   $144.9892   $144.99   $145.00   $145.00  
  Purchase #4 $226.37   8.122%   $244.7558   $244.76   $244.75   $244.80  
  Purchase #5 $222.68   13.550%   $252.8531   $252.85   $252.85   $252.90  
  Purchase #6 $176.53   10.547%   $195.1486   $195.15   $195.15   $195.10  
  Purchase #7 $82.70   12.695%   $93.1988   $93.20   $93.20   $93.20  
  7 purchase totals = $1,114.39       $1,227.9316   $1,227.93   $1,227.95   $1,228.00