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 $60.54   9.433%   $66.2507   $66.25   $66.25   $66.30  
  Purchase #2 $159.37   8.396%   $172.7507   $172.75   $172.75   $172.80  
  Purchase #3 $22.63   4.688%   $23.6909   $23.69   $23.70   $23.70  
  Purchase #4 $215.75   9.570%   $236.3973   $236.40   $236.40   $236.40  
  Purchase #5 $107.53   7.828%   $115.9474   $115.95   $115.95   $115.90  
  Purchase #6 $163.76   13.145%   $185.2863   $185.29   $185.30   $185.30  
  Purchase #7 $170.44   6.282%   $181.147   $181.15   $181.15   $181.10  
  7 purchase totals = $900.02       $981.4703   $981.48   $981.50   $981.50