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 $33.81   11.693%   $37.7634   $37.76   $37.75   $37.80  
  Purchase #2 $137.53   8.798%   $149.6299   $149.63   $149.65   $149.60  
  Purchase #3 $11.63   12.503%   $13.0841   $13.08   $13.10   $13.10  
  Purchase #4 $206.59   9.605%   $226.433   $226.43   $226.45   $226.40  
  Purchase #5 $248.66   3.577%   $257.5546   $257.55   $257.55   $257.60  
  Purchase #6 $162.57   8.828%   $176.9217   $176.92   $176.90   $176.90  
  Purchase #7 $176.78   6.287%   $187.8942   $187.89   $187.90   $187.90  
  7 purchase totals = $977.57       $1,049.2809   $1,049.26   $1,049.30   $1,049.30