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 $76.65   7.778%   $82.6118   $82.61   $82.60   $82.60  
  Purchase #2 $185.93   3.283%   $192.0341   $192.03   $192.05   $192.00  
  Purchase #3 $155.70   4.330%   $162.4418   $162.44   $162.45   $162.40  
  Purchase #4 $224.70   13.174%   $254.302   $254.30   $254.30   $254.30  
  Purchase #5 $136.36   3.803%   $141.5458   $141.55   $141.55   $141.50  
  Purchase #6 $135.29   7.768%   $145.7993   $145.80   $145.80   $145.80  
  Purchase #7 $66.91   6.116%   $71.0022   $71.00   $71.00   $71.00  
  7 purchase totals = $981.54       $1,049.7370   $1,049.73   $1,049.75   $1,049.60