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 $163.69   13.830%   $186.3283   $186.33   $186.35   $186.30  
  Purchase #2 $107.60   12.190%   $120.7164   $120.72   $120.70   $120.70  
  Purchase #3 $248.49   5.605%   $262.4179   $262.42   $262.40   $262.40  
  Purchase #4 $212.42   11.450%   $236.7421   $236.74   $236.75   $236.70  
  Purchase #5 $137.79   3.264%   $142.2875   $142.29   $142.30   $142.30  
  Purchase #6 $208.95   5.851%   $221.1757   $221.18   $221.20   $221.20  
  Purchase #7 $84.71   10.656%   $93.7367   $93.74   $93.75   $93.70  
  7 purchase totals = $1,163.65       $1,263.4046   $1,263.42   $1,263.45   $1,263.30