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 $223.59   5.868%   $236.7103   $236.71   $236.70   $236.70  
  Purchase #2 $232.96   12.832%   $262.8534   $262.85   $262.85   $262.90  
  Purchase #3 $113.53   7.643%   $122.2071   $122.21   $122.20   $122.20  
  Purchase #4 $50.80   4.564%   $53.1185   $53.12   $53.10   $53.10  
  Purchase #5 $185.38   8.688%   $201.4858   $201.49   $201.50   $201.50  
  Purchase #6 $162.77   5.694%   $172.0381   $172.04   $172.05   $172.00  
  Purchase #7 $53.90   3.337%   $55.6986   $55.70   $55.70   $55.70  
  7 purchase totals = $1,022.93       $1,104.1118   $1,104.12   $1,104.10   $1,104.10