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 $49.40   4.433%   $51.5899   $51.59   $51.60   $51.60  
  Purchase #2 $223.27   13.292%   $252.947   $252.95   $252.95   $252.90  
  Purchase #3 $106.29   4.608%   $111.1878   $111.19   $111.20   $111.20  
  Purchase #4 $36.92   11.215%   $41.0606   $41.06   $41.05   $41.10  
  Purchase #5 $108.60   9.352%   $118.7563   $118.76   $118.75   $118.80  
  Purchase #6 $40.49   4.458%   $42.295   $42.30   $42.30   $42.30  
  Purchase #7 $202.59   7.796%   $218.3839   $218.38   $218.40   $218.40  
  7 purchase totals = $767.56       $836.2205   $836.23   $836.25   $836.30