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 $31.73   9.206%   $34.6511   $34.65   $34.65   $34.70  
  Purchase #2 $164.56   6.398%   $175.0885   $175.09   $175.10   $175.10  
  Purchase #3 $92.67   3.219%   $95.653   $95.65   $95.65   $95.70  
  Purchase #4 $222.90   8.346%   $241.5032   $241.50   $241.50   $241.50  
  Purchase #5 $161.69   8.470%   $175.3851   $175.39   $175.40   $175.40  
  Purchase #6 $64.27   8.375%   $69.6526   $69.65   $69.65   $69.70  
  Purchase #7 $233.77   11.807%   $261.3712   $261.37   $261.35   $261.40  
  7 purchase totals = $971.59       $1,053.3047   $1,053.30   $1,053.30   $1,053.50