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 $31.68   5.570%   $33.4446   $33.44   $33.45   $33.40  
  Purchase #2 $54.63   3.577%   $56.5841   $56.58   $56.60   $56.60  
  Purchase #3 $104.33   13.283%   $118.1882   $118.19   $118.20   $118.20  
  Purchase #4 $188.49   6.680%   $201.0811   $201.08   $201.10   $201.10  
  Purchase #5 $79.66   9.204%   $86.9919   $86.99   $87.00   $87.00  
  Purchase #6 $82.97   11.530%   $92.5364   $92.54   $92.55   $92.50  
  Purchase #7 $32.83   4.337%   $34.2538   $34.25   $34.25   $34.30  
  7 purchase totals = $574.59       $623.0801   $623.07   $623.15   $623.10