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 $238.55   3.236%   $246.2695   $246.27   $246.25   $246.30  
  Purchase #2 $76.60   9.217%   $83.6602   $83.66   $83.65   $83.70  
  Purchase #3 $124.27   13.395%   $140.916   $140.92   $140.90   $140.90  
  Purchase #4 $240.69   13.443%   $273.046   $273.05   $273.05   $273.00  
  Purchase #5 $168.63   4.144%   $175.618   $175.62   $175.60   $175.60  
  Purchase #6 $248.35   3.316%   $256.5853   $256.59   $256.60   $256.60  
  Purchase #7 $176.41   7.136%   $188.9986   $189.00   $189.00   $189.00  
  7 purchase totals = $1,273.50       $1,365.0936   $1,365.11   $1,365.05   $1,365.10