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 $249.98   3.805%   $259.4917   $259.49   $259.50   $259.50  
  Purchase #2 $175.72   10.591%   $194.3305   $194.33   $194.35   $194.30  
  Purchase #3 $34.85   5.145%   $36.643   $36.64   $36.65   $36.60  
  Purchase #4 $114.93   11.128%   $127.7194   $127.72   $127.70   $127.70  
  Purchase #5 $234.49   13.822%   $266.9012   $266.90   $266.90   $266.90  
  Purchase #6 $143.54   6.316%   $152.606   $152.61   $152.60   $152.60  
  Purchase #7 $238.51   10.846%   $264.3788   $264.38   $264.40   $264.40  
  7 purchase totals = $1,192.02       $1,302.0706   $1,302.07   $1,302.10   $1,302.00