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 $54.67   3.325%   $56.4878   $56.49   $56.50   $56.50  
  Purchase #2 $100.77   8.815%   $109.6529   $109.65   $109.65   $109.70  
  Purchase #3 $182.64   5.814%   $193.2587   $193.26   $193.25   $193.30  
  Purchase #4 $162.74   8.804%   $177.0676   $177.07   $177.05   $177.10  
  Purchase #5 $176.63   3.594%   $182.9781   $182.98   $183.00   $183.00  
  Purchase #6 $191.78   5.654%   $202.6232   $202.62   $202.60   $202.60  
  Purchase #7 $218.99   9.218%   $239.1765   $239.18   $239.20   $239.20  
  7 purchase totals = $1,088.22       $1,161.2448   $1,161.25   $1,161.25   $1,161.40