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 $17.76   7.247%   $19.0471   $19.05   $19.05   $19.00  
  Purchase #2 $232.98   10.684%   $257.8716   $257.87   $257.85   $257.90  
  Purchase #3 $170.51   3.324%   $176.1778   $176.18   $176.20   $176.20  
  Purchase #4 $164.59   12.433%   $185.0535   $185.05   $185.05   $185.10  
  Purchase #5 $24.65   5.388%   $25.9781   $25.98   $26.00   $26.00  
  Purchase #6 $236.89   13.547%   $268.9815   $268.98   $269.00   $269.00  
  Purchase #7 $116.94   7.169%   $125.3234   $125.32   $125.30   $125.30  
  7 purchase totals = $964.32       $1,058.4330   $1,058.43   $1,058.45   $1,058.50