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 $228.99   13.318%   $259.4869   $259.49   $259.50   $259.50  
  Purchase #2 $114.74   10.276%   $126.5307   $126.53   $126.55   $126.50  
  Purchase #3 $211.65   6.534%   $225.4792   $225.48   $225.50   $225.50  
  Purchase #4 $240.86   3.189%   $248.541   $248.54   $248.55   $248.50  
  Purchase #5 $173.51   11.705%   $193.8193   $193.82   $193.80   $193.80  
  Purchase #6 $9.95   8.238%   $10.7697   $10.77   $10.75   $10.80  
  Purchase #7 $43.86   7.194%   $47.0153   $47.02   $47.00   $47.00  
  7 purchase totals = $1,023.56       $1,111.6421   $1,111.65   $1,111.65   $1,111.60