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 $208.41   13.547%   $236.6433   $236.64   $236.65   $236.60  
  Purchase #2 $159.37   10.358%   $175.8775   $175.88   $175.90   $175.90  
  Purchase #3 $53.55   5.696%   $56.6002   $56.60   $56.60   $56.60  
  Purchase #4 $128.46   4.429%   $134.1495   $134.15   $134.15   $134.10  
  Purchase #5 $233.76   12.176%   $262.2226   $262.22   $262.20   $262.20  
  Purchase #6 $132.41   6.703%   $141.2854   $141.29   $141.30   $141.30  
  Purchase #7 $21.29   12.672%   $23.9879   $23.99   $24.00   $24.00  
  7 purchase totals = $937.25       $1,030.7664   $1,030.77   $1,030.80   $1,030.70