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 $176.46   10.821%   $195.5547   $195.55   $195.55   $195.60  
  Purchase #2 $213.76   4.629%   $223.655   $223.66   $223.65   $223.70  
  Purchase #3 $23.76   4.838%   $24.9095   $24.91   $24.90   $24.90  
  Purchase #4 $24.78   13.366%   $28.0921   $28.09   $28.10   $28.10  
  Purchase #5 $248.74   8.394%   $269.6192   $269.62   $269.60   $269.60  
  Purchase #6 $16.39   13.501%   $18.6028   $18.60   $18.60   $18.60  
  Purchase #7 $120.67   7.479%   $129.6949   $129.69   $129.70   $129.70  
  7 purchase totals = $824.56       $890.1282   $890.12   $890.10   $890.20