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 $248.71   11.467%   $277.2296   $277.23   $277.25   $277.20  
  Purchase #2 $188.36   10.867%   $208.8291   $208.83   $208.85   $208.80  
  Purchase #3 $182.51   7.310%   $195.8515   $195.85   $195.85   $195.90  
  Purchase #4 $221.78   6.704%   $236.6481   $236.65   $236.65   $236.60  
  Purchase #5 $197.80   12.847%   $223.2114   $223.21   $223.20   $223.20  
  Purchase #6 $175.37   8.370%   $190.0485   $190.05   $190.05   $190.00  
  Purchase #7 $68.84   11.633%   $76.8482   $76.85   $76.85   $76.80  
  7 purchase totals = $1,283.37       $1,408.6664   $1,408.67   $1,408.70   $1,408.50