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 $162.89   9.618%   $178.5568   $178.56   $178.55   $178.60  
  Purchase #2 $91.69   4.358%   $95.6859   $95.69   $95.70   $95.70  
  Purchase #3 $64.48   3.858%   $66.9676   $66.97   $66.95   $67.00  
  Purchase #4 $232.43   8.282%   $251.6799   $251.68   $251.70   $251.70  
  Purchase #5 $105.76   9.110%   $115.3947   $115.39   $115.40   $115.40  
  Purchase #6 $246.58   7.499%   $265.071   $265.07   $265.05   $265.10  
  Purchase #7 $226.78   9.633%   $248.6257   $248.63   $248.65   $248.60  
  7 purchase totals = $1,130.61       $1,221.9816   $1,221.99   $1,222.00   $1,222.10