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 $163.76   9.822%   $179.8445   $179.84   $179.85   $179.80  
  Purchase #2 $53.55   5.269%   $56.3715   $56.37   $56.35   $56.40  
  Purchase #3 $89.49   4.215%   $93.262   $93.26   $93.25   $93.30  
  Purchase #4 $240.76   6.195%   $255.6751   $255.68   $255.70   $255.70  
  Purchase #5 $201.62   12.858%   $227.5443   $227.54   $227.55   $227.50  
  Purchase #6 $86.61   9.227%   $94.6015   $94.60   $94.60   $94.60  
  Purchase #7 $179.63   7.175%   $192.5185   $192.52   $192.50   $192.50  
  7 purchase totals = $1,015.42       $1,099.8174   $1,099.81   $1,099.80   $1,099.80