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 $245.48   13.573%   $278.799   $278.80   $278.80   $278.80  
  Purchase #2 $34.75   5.353%   $36.6102   $36.61   $36.60   $36.60  
  Purchase #3 $57.61   8.815%   $62.6883   $62.69   $62.70   $62.70  
  Purchase #4 $249.90   9.709%   $274.1628   $274.16   $274.15   $274.20  
  Purchase #5 $64.73   6.694%   $69.063   $69.06   $69.05   $69.10  
  Purchase #6 $113.72   9.614%   $124.653   $124.65   $124.65   $124.70  
  Purchase #7 $163.51   10.492%   $180.6655   $180.67   $180.65   $180.70  
  7 purchase totals = $929.70       $1,026.6418   $1,026.64   $1,026.60   $1,026.80