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 $176.49   5.717%   $186.5799   $186.58   $186.60   $186.60  
  Purchase #2 $31.44   3.786%   $32.6303   $32.63   $32.65   $32.60  
  Purchase #3 $21.80   6.808%   $23.2841   $23.28   $23.30   $23.30  
  Purchase #4 $116.78   6.508%   $124.38   $124.38   $124.40   $124.40  
  Purchase #5 $148.30   12.591%   $166.9725   $166.97   $166.95   $167.00  
  Purchase #6 $218.81   5.293%   $230.3916   $230.39   $230.40   $230.40  
  Purchase #7 $186.58   9.423%   $204.1614   $204.16   $204.15   $204.20  
  7 purchase totals = $900.20       $968.3998   $968.39   $968.45   $968.50