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 $115.51   8.569%   $125.4081   $125.41   $125.40   $125.40  
  Purchase #2 $93.87   10.393%   $103.6259   $103.63   $103.65   $103.60  
  Purchase #3 $28.73   11.542%   $32.046   $32.05   $32.05   $32.00  
  Purchase #4 $245.99   10.105%   $270.8473   $270.85   $270.85   $270.80  
  Purchase #5 $246.31   9.403%   $269.4705   $269.47   $269.45   $269.50  
  Purchase #6 $192.93   4.535%   $201.6794   $201.68   $201.70   $201.70  
  Purchase #7 $161.93   5.669%   $171.1098   $171.11   $171.10   $171.10  
  7 purchase totals = $1,085.27       $1,174.1870   $1,174.20   $1,174.20   $1,174.10