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 $218.81   9.333%   $239.2315   $239.23   $239.25   $239.20  
  Purchase #2 $131.69   11.855%   $147.3018   $147.30   $147.30   $147.30  
  Purchase #3 $197.68   3.721%   $205.0357   $205.04   $205.05   $205.00  
  Purchase #4 $32.32   12.759%   $36.4437   $36.44   $36.45   $36.40  
  Purchase #5 $58.42   12.672%   $65.823   $65.82   $65.80   $65.80  
  Purchase #6 $222.35   6.384%   $236.5448   $236.54   $236.55   $236.50  
  Purchase #7 $241.95   10.538%   $267.4467   $267.45   $267.45   $267.40  
  7 purchase totals = $1,103.22       $1,197.8272   $1,197.82   $1,197.85   $1,197.60