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 $161.49   13.274%   $182.9262   $182.93   $182.95   $182.90  
  Purchase #2 $187.68   3.168%   $193.6257   $193.63   $193.65   $193.60  
  Purchase #3 $231.74   8.313%   $251.0045   $251.00   $251.00   $251.00  
  Purchase #4 $38.37   6.542%   $40.8802   $40.88   $40.90   $40.90  
  Purchase #5 $110.83   4.803%   $116.1532   $116.15   $116.15   $116.20  
  Purchase #6 $182.71   8.474%   $198.1928   $198.19   $198.20   $198.20  
  Purchase #7 $143.96   9.348%   $157.4174   $157.42   $157.40   $157.40  
  7 purchase totals = $1,056.78       $1,140.2000   $1,140.20   $1,140.25   $1,140.20