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 $208.59   11.740%   $233.0785   $233.08   $233.10   $233.10  
  Purchase #2 $107.73   10.714%   $119.2722   $119.27   $119.25   $119.30  
  Purchase #3 $242.52   3.870%   $251.9055   $251.91   $251.90   $251.90  
  Purchase #4 $188.38   13.211%   $213.2669   $213.27   $213.25   $213.30  
  Purchase #5 $66.91   4.261%   $69.761   $69.76   $69.75   $69.80  
  Purchase #6 $35.70   7.708%   $38.4518   $38.45   $38.45   $38.50  
  Purchase #7 $237.28   11.230%   $263.9265   $263.93   $263.95   $263.90  
  7 purchase totals = $1,087.11       $1,189.6624   $1,189.67   $1,189.65   $1,189.80