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 $104.80   9.110%   $114.3473   $114.35   $114.35   $114.30  
  Purchase #2 $51.45   10.483%   $56.8435   $56.84   $56.85   $56.80  
  Purchase #3 $177.96   8.287%   $192.7075   $192.71   $192.70   $192.70  
  Purchase #4 $80.41   7.810%   $86.69   $86.69   $86.70   $86.70  
  Purchase #5 $177.90   5.369%   $187.4515   $187.45   $187.45   $187.50  
  Purchase #6 $59.67   4.664%   $62.453   $62.45   $62.45   $62.50  
  Purchase #7 $176.38   9.456%   $193.0585   $193.06   $193.05   $193.10  
  7 purchase totals = $828.57       $893.5513   $893.55   $893.55   $893.60