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 $186.68   11.871%   $208.8408   $208.84   $208.85   $208.80  
  Purchase #2 $197.67   7.719%   $212.9281   $212.93   $212.95   $212.90  
  Purchase #3 $171.99   9.229%   $187.863   $187.86   $187.85   $187.90  
  Purchase #4 $228.72   5.794%   $241.972   $241.97   $241.95   $242.00  
  Purchase #5 $71.83   6.279%   $76.3402   $76.34   $76.35   $76.30  
  Purchase #6 $183.40   4.833%   $192.2637   $192.26   $192.25   $192.30  
  Purchase #7 $7.99   5.122%   $8.3992   $8.40   $8.40   $8.40  
  7 purchase totals = $1,048.28       $1,128.6070   $1,128.60   $1,128.60   $1,128.60