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 $201.31   12.462%   $226.3973   $226.40   $226.40   $226.40  
  Purchase #2 $59.39   10.657%   $65.7192   $65.72   $65.70   $65.70  
  Purchase #3 $28.83   5.816%   $30.5068   $30.51   $30.50   $30.50  
  Purchase #4 $242.92   12.556%   $273.421   $273.42   $273.40   $273.40  
  Purchase #5 $152.65   8.297%   $165.3154   $165.32   $165.30   $165.30  
  Purchase #6 $27.93   3.526%   $28.9148   $28.91   $28.90   $28.90  
  Purchase #7 $215.92   8.522%   $234.3207   $234.32   $234.30   $234.30  
  7 purchase totals = $928.95       $1,024.5952   $1,024.60   $1,024.50   $1,024.50