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 $152.97   8.574%   $166.0856   $166.09   $166.10   $166.10  
  Purchase #2 $192.58   8.451%   $208.8549   $208.85   $208.85   $208.90  
  Purchase #3 $241.85   4.746%   $253.3282   $253.33   $253.35   $253.30  
  Purchase #4 $110.31   6.578%   $117.5662   $117.57   $117.55   $117.60  
  Purchase #5 $136.28   3.274%   $140.7418   $140.74   $140.75   $140.70  
  Purchase #6 $44.30   6.408%   $47.1387   $47.14   $47.15   $47.10  
  Purchase #7 $22.59   10.248%   $24.905   $24.91   $24.90   $24.90  
  7 purchase totals = $900.88       $958.6204   $958.63   $958.65   $958.60