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 $22.57   8.772%   $24.5498   $24.55   $24.55   $24.50  
  Purchase #2 $205.79   13.315%   $233.1909   $233.19   $233.20   $233.20  
  Purchase #3 $202.32   9.311%   $221.158   $221.16   $221.15   $221.20  
  Purchase #4 $76.50   5.333%   $80.5797   $80.58   $80.60   $80.60  
  Purchase #5 $248.56   3.422%   $257.0657   $257.07   $257.05   $257.10  
  Purchase #6 $190.70   9.431%   $208.6849   $208.68   $208.70   $208.70  
  Purchase #7 $12.87   13.601%   $14.6204   $14.62   $14.60   $14.60  
  7 purchase totals = $959.31       $1,039.8494   $1,039.85   $1,039.85   $1,039.90