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 $68.62   7.246%   $73.5922   $73.59   $73.60   $73.60  
  Purchase #2 $244.44   13.424%   $277.2536   $277.25   $277.25   $277.30  
  Purchase #3 $94.61   13.154%   $107.055   $107.06   $107.05   $107.10  
  Purchase #4 $163.69   9.708%   $179.581   $179.58   $179.60   $179.60  
  Purchase #5 $185.36   5.508%   $195.5696   $195.57   $195.55   $195.60  
  Purchase #6 $93.46   8.794%   $101.6789   $101.68   $101.70   $101.70  
  Purchase #7 $59.82   9.646%   $65.5902   $65.59   $65.60   $65.60  
  7 purchase totals = $910.00       $1,000.3205   $1,000.32   $1,000.35   $1,000.50