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 $238.53   9.791%   $261.8845   $261.88   $261.90   $261.90  
  Purchase #2 $190.98   6.257%   $202.9296   $202.93   $202.95   $202.90  
  Purchase #3 $232.51   5.819%   $246.0398   $246.04   $246.05   $246.00  
  Purchase #4 $233.75   4.162%   $243.4787   $243.48   $243.50   $243.50  
  Purchase #5 $224.30   12.794%   $252.9969   $253.00   $253.00   $253.00  
  Purchase #6 $136.53   6.757%   $145.7553   $145.76   $145.75   $145.80  
  Purchase #7 $78.61   10.463%   $86.835   $86.84   $86.85   $86.80  
  7 purchase totals = $1,335.21       $1,439.9198   $1,439.93   $1,440.00   $1,439.90