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 $205.84   6.183%   $218.5671   $218.57   $218.55   $218.60  
  Purchase #2 $172.63   11.477%   $192.4427   $192.44   $192.45   $192.40  
  Purchase #3 $151.66   5.719%   $160.3334   $160.33   $160.35   $160.30  
  Purchase #4 $248.38   11.117%   $275.9924   $275.99   $276.00   $276.00  
  Purchase #5 $31.59   13.413%   $35.8272   $35.83   $35.85   $35.80  
  Purchase #6 $37.55   10.554%   $41.513   $41.51   $41.50   $41.50  
  Purchase #7 $132.84   7.723%   $143.0992   $143.10   $143.10   $143.10  
  7 purchase totals = $980.49       $1,067.7750   $1,067.77   $1,067.80   $1,067.70