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 $230.55   13.366%   $261.3653   $261.37   $261.35   $261.40  
  Purchase #2 $111.25   9.155%   $121.4349   $121.43   $121.45   $121.40  
  Purchase #3 $221.75   10.339%   $244.6767   $244.68   $244.70   $244.70  
  Purchase #4 $132.51   3.337%   $136.9319   $136.93   $136.95   $136.90  
  Purchase #5 $77.34   4.484%   $80.8079   $80.81   $80.80   $80.80  
  Purchase #6 $11.89   13.482%   $13.493   $13.49   $13.50   $13.50  
  Purchase #7 $168.98   12.564%   $190.2106   $190.21   $190.20   $190.20  
  7 purchase totals = $954.27       $1,048.9203   $1,048.92   $1,048.95   $1,048.90