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 $179.47   10.463%   $198.2479   $198.25   $198.25   $198.20  
  Purchase #2 $168.72   13.113%   $190.8443   $190.84   $190.85   $190.80  
  Purchase #3 $21.83   7.136%   $23.3878   $23.39   $23.40   $23.40  
  Purchase #4 $122.43   6.368%   $130.2263   $130.23   $130.25   $130.20  
  Purchase #5 $67.36   8.736%   $73.2446   $73.24   $73.25   $73.20  
  Purchase #6 $205.97   13.252%   $233.2651   $233.27   $233.25   $233.30  
  Purchase #7 $205.81   6.201%   $218.5723   $218.57   $218.55   $218.60  
  7 purchase totals = $971.59       $1,067.7883   $1,067.79   $1,067.80   $1,067.70