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 $236.89   4.602%   $247.7917   $247.79   $247.80   $247.80  
  Purchase #2 $213.79   8.853%   $232.7168   $232.72   $232.70   $232.70  
  Purchase #3 $202.99   7.846%   $218.9166   $218.92   $218.90   $218.90  
  Purchase #4 $144.34   5.726%   $152.6049   $152.60   $152.60   $152.60  
  Purchase #5 $198.40   8.702%   $215.6648   $215.66   $215.65   $215.70  
  Purchase #6 $77.89   8.730%   $84.6898   $84.69   $84.70   $84.70  
  Purchase #7 $78.44   13.823%   $89.2828   $89.28   $89.30   $89.30  
  7 purchase totals = $1,152.74       $1,241.6674   $1,241.66   $1,241.65   $1,241.70