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 $214.60   11.654%   $239.6095   $239.61   $239.60   $239.60  
  Purchase #2 $222.81   4.858%   $233.6341   $233.63   $233.65   $233.60  
  Purchase #3 $22.88   5.495%   $24.1373   $24.14   $24.15   $24.10  
  Purchase #4 $238.68   4.797%   $250.1295   $250.13   $250.15   $250.10  
  Purchase #5 $95.64   9.819%   $105.0309   $105.03   $105.05   $105.00  
  Purchase #6 $245.61   13.475%   $278.7059   $278.71   $278.70   $278.70  
  Purchase #7 $131.30   12.528%   $147.7493   $147.75   $147.75   $147.70  
  7 purchase totals = $1,171.52       $1,278.9965   $1,279.00   $1,279.05   $1,278.80