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 $119.62   3.144%   $123.3809   $123.38   $123.40   $123.40  
  Purchase #2 $221.28   11.120%   $245.8863   $245.89   $245.90   $245.90  
  Purchase #3 $162.97   12.631%   $183.5547   $183.55   $183.55   $183.60  
  Purchase #4 $174.60   6.803%   $186.478   $186.48   $186.50   $186.50  
  Purchase #5 $116.39   7.194%   $124.7631   $124.76   $124.75   $124.80  
  Purchase #6 $228.70   13.847%   $260.3681   $260.37   $260.35   $260.40  
  Purchase #7 $137.86   4.371%   $143.8859   $143.89   $143.90   $143.90  
  7 purchase totals = $1,161.42       $1,268.3170   $1,268.32   $1,268.35   $1,268.50