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 $232.25   12.595%   $261.5019   $261.50   $261.50   $261.50  
  Purchase #2 $21.86   12.644%   $24.624   $24.62   $24.60   $24.60  
  Purchase #3 $29.96   9.515%   $32.8107   $32.81   $32.80   $32.80  
  Purchase #4 $192.35   4.330%   $200.6788   $200.68   $200.70   $200.70  
  Purchase #5 $106.55   7.819%   $114.8811   $114.88   $114.90   $114.90  
  Purchase #6 $92.51   4.858%   $97.0041   $97.00   $97.00   $97.00  
  Purchase #7 $240.54   6.289%   $255.6676   $255.67   $255.65   $255.70  
  7 purchase totals = $916.02       $987.1682   $987.16   $987.15   $987.20