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 $114.89   9.697%   $126.0309   $126.03   $126.05   $126.00  
  Purchase #2 $38.39   10.147%   $42.2854   $42.29   $42.30   $42.30  
  Purchase #3 $223.83   9.531%   $245.1632   $245.16   $245.15   $245.20  
  Purchase #4 $32.42   11.630%   $36.1904   $36.19   $36.20   $36.20  
  Purchase #5 $38.45   6.416%   $40.917   $40.92   $40.90   $40.90  
  Purchase #6 $209.85   13.425%   $238.0224   $238.02   $238.00   $238.00  
  Purchase #7 $226.62   5.789%   $239.739   $239.74   $239.75   $239.70  
  7 purchase totals = $884.45       $968.3483   $968.35   $968.35   $968.30