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 $187.97   9.860%   $206.5038   $206.50   $206.50   $206.50  
  Purchase #2 $186.48   3.304%   $192.6413   $192.64   $192.65   $192.60  
  Purchase #3 $26.65   10.262%   $29.3848   $29.38   $29.40   $29.40  
  Purchase #4 $236.35   9.771%   $259.4438   $259.44   $259.45   $259.40  
  Purchase #5 $50.78   10.680%   $56.2033   $56.20   $56.20   $56.20  
  Purchase #6 $8.40   13.861%   $9.5643   $9.56   $9.55   $9.60  
  Purchase #7 $109.54   7.339%   $117.5791   $117.58   $117.60   $117.60  
  7 purchase totals = $806.17       $871.3204   $871.30   $871.35   $871.30