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 $222.68   13.857%   $253.5368   $253.54   $253.55   $253.50  
  Purchase #2 $177.32   12.667%   $199.7811   $199.78   $199.80   $199.80  
  Purchase #3 $18.51   7.388%   $19.8775   $19.88   $19.90   $19.90  
  Purchase #4 $171.81   9.455%   $188.0546   $188.05   $188.05   $188.10  
  Purchase #5 $76.41   12.444%   $85.9185   $85.92   $85.90   $85.90  
  Purchase #6 $64.77   3.833%   $67.2526   $67.25   $67.25   $67.30  
  Purchase #7 $205.45   3.318%   $212.2668   $212.27   $212.25   $212.30  
  7 purchase totals = $936.95       $1,026.6879   $1,026.69   $1,026.70   $1,026.80