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 $95.26   3.731%   $98.8142   $98.81   $98.80   $98.80  
  Purchase #2 $135.90   4.352%   $141.8144   $141.81   $141.80   $141.80  
  Purchase #3 $73.44   5.197%   $77.2567   $77.26   $77.25   $77.30  
  Purchase #4 $53.58   13.129%   $60.6145   $60.61   $60.60   $60.60  
  Purchase #5 $157.54   6.684%   $168.07   $168.07   $168.05   $168.10  
  Purchase #6 $186.55   3.453%   $192.9916   $192.99   $193.00   $193.00  
  Purchase #7 $28.83   13.657%   $32.7673   $32.77   $32.75   $32.80  
  7 purchase totals = $731.10       $772.3287   $772.32   $772.25   $772.40