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 $56.65   7.118%   $60.6823   $60.68   $60.70   $60.70  
  Purchase #2 $94.75   12.517%   $106.6099   $106.61   $106.60   $106.60  
  Purchase #3 $222.85   7.644%   $239.8847   $239.88   $239.90   $239.90  
  Purchase #4 $171.83   8.595%   $186.5988   $186.60   $186.60   $186.60  
  Purchase #5 $66.94   11.482%   $74.6261   $74.63   $74.65   $74.60  
  Purchase #6 $170.63   13.398%   $193.491   $193.49   $193.50   $193.50  
  Purchase #7 $200.55   7.332%   $215.2543   $215.25   $215.25   $215.30  
  7 purchase totals = $984.20       $1,077.1471   $1,077.14   $1,077.20   $1,077.20