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 $123.76   12.322%   $139.0097   $139.01   $139.00   $139.00  
  Purchase #2 $21.29   11.535%   $23.7458   $23.75   $23.75   $23.70  
  Purchase #3 $126.74   11.866%   $141.779   $141.78   $141.80   $141.80  
  Purchase #4 $115.31   7.255%   $123.6757   $123.68   $123.70   $123.70  
  Purchase #5 $198.57   5.246%   $208.987   $208.99   $209.00   $209.00  
  Purchase #6 $189.81   12.123%   $212.8207   $212.82   $212.80   $212.80  
  Purchase #7 $196.53   9.207%   $214.6245   $214.62   $214.60   $214.60  
  7 purchase totals = $972.01       $1,064.6424   $1,064.65   $1,064.65   $1,064.60