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 $60.41   13.815%   $68.7556   $68.76   $68.75   $68.80  
  Purchase #2 $22.79   5.840%   $24.1209   $24.12   $24.10   $24.10  
  Purchase #3 $73.25   13.207%   $82.9241   $82.92   $82.90   $82.90  
  Purchase #4 $85.31   9.586%   $93.4878   $93.49   $93.50   $93.50  
  Purchase #5 $100.88   6.644%   $107.5825   $107.58   $107.60   $107.60  
  Purchase #6 $92.64   10.202%   $102.0911   $102.09   $102.10   $102.10  
  Purchase #7 $198.78   7.786%   $214.257   $214.26   $214.25   $214.30  
  7 purchase totals = $634.06       $693.2190   $693.22   $693.20   $693.30