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 $226.28   6.530%   $241.0561   $241.06   $241.05   $241.10  
  Purchase #2 $84.38   13.391%   $95.6793   $95.68   $95.70   $95.70  
  Purchase #3 $105.55   11.467%   $117.6534   $117.65   $117.65   $117.70  
  Purchase #4 $242.71   13.114%   $274.539   $274.54   $274.55   $274.50  
  Purchase #5 $67.35   10.332%   $74.3086   $74.31   $74.30   $74.30  
  Purchase #6 $207.81   12.340%   $233.4538   $233.45   $233.45   $233.50  
  Purchase #7 $89.44   8.719%   $97.2383   $97.24   $97.25   $97.20  
  7 purchase totals = $1,023.52       $1,133.9285   $1,133.93   $1,133.95   $1,134.00