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 $185.69   3.557%   $192.295   $192.30   $192.30   $192.30  
  Purchase #2 $60.95   5.105%   $64.0615   $64.06   $64.05   $64.10  
  Purchase #3 $64.45   7.419%   $69.2315   $69.23   $69.25   $69.20  
  Purchase #4 $231.54   7.273%   $248.3799   $248.38   $248.40   $248.40  
  Purchase #5 $102.40   10.137%   $112.7803   $112.78   $112.80   $112.80  
  Purchase #6 $73.89   5.303%   $77.8084   $77.81   $77.80   $77.80  
  Purchase #7 $247.39   11.681%   $276.2876   $276.29   $276.30   $276.30  
  7 purchase totals = $966.31       $1,040.8442   $1,040.85   $1,040.90   $1,040.90