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 $24.30   9.401%   $26.5844   $26.58   $26.60   $26.60  
  Purchase #2 $205.33   8.531%   $222.8467   $222.85   $222.85   $222.80  
  Purchase #3 $70.64   8.272%   $76.4833   $76.48   $76.50   $76.50  
  Purchase #4 $15.71   13.698%   $17.862   $17.86   $17.85   $17.90  
  Purchase #5 $80.74   11.844%   $90.3028   $90.30   $90.30   $90.30  
  Purchase #6 $218.62   10.704%   $242.0211   $242.02   $242.00   $242.00  
  Purchase #7 $168.58   5.626%   $178.0643   $178.06   $178.05   $178.10  
  7 purchase totals = $783.92       $854.1646   $854.15   $854.15   $854.20