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 $43.49   13.721%   $49.4573   $49.46   $49.45   $49.50  
  Purchase #2 $225.76   9.260%   $246.6654   $246.67   $246.65   $246.70  
  Purchase #3 $220.99   5.685%   $233.5533   $233.55   $233.55   $233.60  
  Purchase #4 $69.35   11.408%   $77.2614   $77.26   $77.25   $77.30  
  Purchase #5 $62.39   6.527%   $66.4622   $66.46   $66.45   $66.50  
  Purchase #6 $225.40   8.277%   $244.0564   $244.06   $244.05   $244.10  
  Purchase #7 $57.80   11.238%   $64.2956   $64.30   $64.30   $64.30  
  7 purchase totals = $905.18       $981.7516   $981.76   $981.70   $982.00