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 $245.54   12.786%   $276.9347   $276.93   $276.95   $276.90  
  Purchase #2 $224.55   13.213%   $254.2198   $254.22   $254.20   $254.20  
  Purchase #3 $244.47   7.380%   $262.5119   $262.51   $262.50   $262.50  
  Purchase #4 $193.78   3.666%   $200.884   $200.88   $200.90   $200.90  
  Purchase #5 $119.73   8.607%   $130.0352   $130.04   $130.05   $130.00  
  Purchase #6 $231.46   13.182%   $261.9711   $261.97   $261.95   $262.00  
  Purchase #7 $25.78   4.839%   $27.0275   $27.03   $27.05   $27.00  
  7 purchase totals = $1,285.31       $1,413.5842   $1,413.58   $1,413.60   $1,413.50