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 $192.68   12.240%   $216.264   $216.26   $216.25   $216.30  
  Purchase #2 $37.89   13.565%   $43.0298   $43.03   $43.05   $43.00  
  Purchase #3 $144.41   8.827%   $157.1571   $157.16   $157.15   $157.20  
  Purchase #4 $127.39   8.232%   $137.8767   $137.88   $137.90   $137.90  
  Purchase #5 $130.77   3.581%   $135.4529   $135.45   $135.45   $135.50  
  Purchase #6 $243.84   6.488%   $259.6603   $259.66   $259.65   $259.70  
  Purchase #7 $120.29   3.156%   $124.0864   $124.09   $124.10   $124.10  
  7 purchase totals = $997.27       $1,073.5272   $1,073.53   $1,073.55   $1,073.70