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 $208.53   8.229%   $225.6899   $225.69   $225.70   $225.70  
  Purchase #2 $193.57   9.313%   $211.5972   $211.60   $211.60   $211.60  
  Purchase #3 $213.36   13.196%   $241.515   $241.52   $241.50   $241.50  
  Purchase #4 $250.59   5.804%   $265.1342   $265.13   $265.15   $265.10  
  Purchase #5 $173.44   8.124%   $187.5303   $187.53   $187.55   $187.50  
  Purchase #6 $151.30   6.699%   $161.4356   $161.44   $161.45   $161.40  
  Purchase #7 $15.91   4.261%   $16.5879   $16.59   $16.60   $16.60  
  7 purchase totals = $1,206.70       $1,309.4901   $1,309.50   $1,309.55   $1,309.40