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 $238.76   6.671%   $254.6877   $254.69   $254.70   $254.70  
  Purchase #2 $215.77   11.786%   $241.2007   $241.20   $241.20   $241.20  
  Purchase #3 $35.70   6.219%   $37.9202   $37.92   $37.90   $37.90  
  Purchase #4 $183.75   9.652%   $201.4856   $201.49   $201.50   $201.50  
  Purchase #5 $30.80   12.563%   $34.6694   $34.67   $34.65   $34.70  
  Purchase #6 $237.93   9.727%   $261.0735   $261.07   $261.05   $261.10  
  Purchase #7 $230.81   4.525%   $241.2542   $241.25   $241.25   $241.30  
  7 purchase totals = $1,173.52       $1,272.2913   $1,272.29   $1,272.25   $1,272.40