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 $153.32   8.390%   $166.1835   $166.18   $166.20   $166.20  
  Purchase #2 $187.74   3.293%   $193.9223   $193.92   $193.90   $193.90  
  Purchase #3 $29.96   10.164%   $33.0051   $33.01   $33.00   $33.00  
  Purchase #4 $121.92   11.545%   $135.9957   $136.00   $136.00   $136.00  
  Purchase #5 $17.25   6.543%   $18.3787   $18.38   $18.40   $18.40  
  Purchase #6 $186.99   3.805%   $194.105   $194.11   $194.10   $194.10  
  Purchase #7 $133.72   5.743%   $141.3995   $141.40   $141.40   $141.40  
  7 purchase totals = $830.90       $882.9898   $883.00   $883.00   $883.00