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 $144.95   11.858%   $162.1382   $162.14   $162.15   $162.10  
  Purchase #2 $222.54   9.323%   $243.2874   $243.29   $243.30   $243.30  
  Purchase #3 $127.46   10.384%   $140.6954   $140.70   $140.70   $140.70  
  Purchase #4 $157.54   4.562%   $164.727   $164.73   $164.75   $164.70  
  Purchase #5 $75.72   3.328%   $78.24   $78.24   $78.25   $78.20  
  Purchase #6 $70.77   3.598%   $73.3163   $73.32   $73.30   $73.30  
  Purchase #7 $160.99   6.738%   $171.8375   $171.84   $171.85   $171.80  
  7 purchase totals = $959.97       $1,034.2418   $1,034.26   $1,034.30   $1,034.10