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 $221.84   6.518%   $236.2995   $236.30   $236.30   $236.30  
  Purchase #2 $206.61   4.686%   $216.2917   $216.29   $216.30   $216.30  
  Purchase #3 $248.28   13.856%   $282.6817   $282.68   $282.70   $282.70  
  Purchase #4 $201.39   11.397%   $224.3424   $224.34   $224.35   $224.30  
  Purchase #5 $237.66   12.835%   $268.1637   $268.16   $268.15   $268.20  
  Purchase #6 $16.94   12.353%   $19.0326   $19.03   $19.05   $19.00  
  Purchase #7 $101.27   4.526%   $105.8535   $105.85   $105.85   $105.90  
  7 purchase totals = $1,233.99       $1,352.6651   $1,352.65   $1,352.70   $1,352.70