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 $192.42   3.561%   $199.2721   $199.27   $199.25   $199.30  
  Purchase #2 $176.72   9.525%   $193.5526   $193.55   $193.55   $193.60  
  Purchase #3 $188.42   7.409%   $202.38   $202.38   $202.40   $202.40  
  Purchase #4 $110.69   13.182%   $125.2812   $125.28   $125.30   $125.30  
  Purchase #5 $104.99   13.292%   $118.9453   $118.95   $118.95   $118.90  
  Purchase #6 $179.73   3.308%   $185.6755   $185.68   $185.70   $185.70  
  Purchase #7 $42.25   9.376%   $46.2114   $46.21   $46.20   $46.20  
  7 purchase totals = $995.22       $1,071.3181   $1,071.32   $1,071.35   $1,071.40