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 $140.51   13.591%   $159.6067   $159.61   $159.60   $159.60  
  Purchase #2 $189.37   8.612%   $205.6785   $205.68   $205.70   $205.70  
  Purchase #3 $28.66   13.367%   $32.491   $32.49   $32.50   $32.50  
  Purchase #4 $232.90   5.402%   $245.4813   $245.48   $245.50   $245.50  
  Purchase #5 $11.61   4.683%   $12.1537   $12.15   $12.15   $12.20  
  Purchase #6 $234.63   11.474%   $261.5514   $261.55   $261.55   $261.60  
  Purchase #7 $185.84   9.164%   $202.8704   $202.87   $202.85   $202.90  
  7 purchase totals = $1,023.52       $1,119.8330   $1,119.83   $1,119.85   $1,120.00