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 $151.53   10.233%   $167.0361   $167.04   $167.05   $167.00  
  Purchase #2 $124.62   12.706%   $140.4542   $140.45   $140.45   $140.50  
  Purchase #3 $183.70   5.601%   $193.989   $193.99   $194.00   $194.00  
  Purchase #4 $138.32   3.634%   $143.3465   $143.35   $143.35   $143.30  
  Purchase #5 $7.63   5.474%   $8.0477   $8.05   $8.05   $8.00  
  Purchase #6 $158.34   3.390%   $163.7077   $163.71   $163.70   $163.70  
  Purchase #7 $147.58   13.672%   $167.7571   $167.76   $167.75   $167.80  
  7 purchase totals = $911.72       $984.3383   $984.35   $984.35   $984.30