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 $228.92   9.332%   $250.2828   $250.28   $250.30   $250.30  
  Purchase #2 $34.66   13.296%   $39.2684   $39.27   $39.25   $39.30  
  Purchase #3 $144.88   8.834%   $157.6787   $157.68   $157.70   $157.70  
  Purchase #4 $68.42   7.566%   $73.5967   $73.60   $73.60   $73.60  
  Purchase #5 $121.43   6.556%   $129.391   $129.39   $129.40   $129.40  
  Purchase #6 $122.32   8.585%   $132.8212   $132.82   $132.80   $132.80  
  Purchase #7 $214.74   12.164%   $240.861   $240.86   $240.85   $240.90  
  7 purchase totals = $935.37       $1,023.8998   $1,023.90   $1,023.90   $1,024.00