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 $166.76   9.683%   $182.9074   $182.91   $182.90   $182.90  
  Purchase #2 $197.70   13.151%   $223.6995   $223.70   $223.70   $223.70  
  Purchase #3 $104.55   11.627%   $116.706   $116.71   $116.70   $116.70  
  Purchase #4 $175.95   5.218%   $185.1311   $185.13   $185.15   $185.10  
  Purchase #5 $176.83   12.307%   $198.5925   $198.59   $198.60   $198.60  
  Purchase #6 $227.82   9.621%   $249.7386   $249.74   $249.75   $249.70  
  Purchase #7 $67.37   13.661%   $76.5734   $76.57   $76.55   $76.60  
  7 purchase totals = $1,116.98       $1,233.3485   $1,233.35   $1,233.35   $1,233.30