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 $236.91   9.716%   $259.9282   $259.93   $259.95   $259.90  
  Purchase #2 $43.57   12.695%   $49.1012   $49.10   $49.10   $49.10  
  Purchase #3 $183.86   12.412%   $206.6807   $206.68   $206.70   $206.70  
  Purchase #4 $58.39   6.358%   $62.1024   $62.10   $62.10   $62.10  
  Purchase #5 $143.51   12.538%   $161.5033   $161.50   $161.50   $161.50  
  Purchase #6 $201.29   11.563%   $224.5652   $224.57   $224.55   $224.60  
  Purchase #7 $101.29   6.711%   $108.0876   $108.09   $108.10   $108.10  
  7 purchase totals = $968.82       $1,071.9686   $1,071.97   $1,072.00   $1,072.00