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 $29.41   9.116%   $32.091   $32.09   $32.10   $32.10  
  Purchase #2 $173.70   7.457%   $186.6528   $186.65   $186.65   $186.70  
  Purchase #3 $161.91   5.711%   $171.1567   $171.16   $171.15   $171.20  
  Purchase #4 $106.58   6.444%   $113.448   $113.45   $113.45   $113.40  
  Purchase #5 $122.42   6.512%   $130.392   $130.39   $130.40   $130.40  
  Purchase #6 $32.68   3.732%   $33.8996   $33.90   $33.90   $33.90  
  Purchase #7 $94.55   4.285%   $98.6015   $98.60   $98.60   $98.60  
  7 purchase totals = $721.25       $766.2416   $766.24   $766.25   $766.30