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 $168.58   13.861%   $191.9469   $191.95   $191.95   $191.90  
  Purchase #2 $120.26   7.344%   $129.0919   $129.09   $129.10   $129.10  
  Purchase #3 $59.66   8.333%   $64.6315   $64.63   $64.65   $64.60  
  Purchase #4 $49.42   12.787%   $55.7393   $55.74   $55.75   $55.70  
  Purchase #5 $158.81   3.190%   $163.876   $163.88   $163.90   $163.90  
  Purchase #6 $42.29   4.615%   $44.2417   $44.24   $44.25   $44.20  
  Purchase #7 $185.97   10.416%   $205.3406   $205.34   $205.35   $205.30  
  7 purchase totals = $784.99       $854.8679   $854.87   $854.95   $854.70