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 $246.50   9.713%   $270.4425   $270.44   $270.45   $270.40  
  Purchase #2 $127.75   3.738%   $132.5253   $132.53   $132.55   $132.50  
  Purchase #3 $24.71   4.585%   $25.843   $25.84   $25.85   $25.80  
  Purchase #4 $86.70   4.424%   $90.5356   $90.54   $90.55   $90.50  
  Purchase #5 $90.28   13.676%   $102.6267   $102.63   $102.65   $102.60  
  Purchase #6 $137.34   10.500%   $151.7607   $151.76   $151.75   $151.80  
  Purchase #7 $208.27   8.688%   $226.3645   $226.36   $226.35   $226.40  
  7 purchase totals = $921.55       $1,000.0983   $1,000.10   $1,000.15   $1,000.00