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 $11.33   12.493%   $12.7455   $12.75   $12.75   $12.70  
  Purchase #2 $66.49   4.477%   $69.4668   $69.47   $69.45   $69.50  
  Purchase #3 $146.83   10.165%   $161.7553   $161.76   $161.75   $161.80  
  Purchase #4 $208.45   9.441%   $228.1298   $228.13   $228.15   $228.10  
  Purchase #5 $159.27   10.528%   $176.0379   $176.04   $176.05   $176.00  
  Purchase #6 $181.54   8.127%   $196.2938   $196.29   $196.30   $196.30  
  Purchase #7 $215.37   7.274%   $231.036   $231.04   $231.05   $231.00  
  7 purchase totals = $989.28       $1,075.4651   $1,075.48   $1,075.50   $1,075.40