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 $239.64   11.521%   $267.2489   $267.25   $267.25   $267.20  
  Purchase #2 $60.26   4.554%   $63.0042   $63.00   $63.00   $63.00  
  Purchase #3 $248.41   3.801%   $257.8521   $257.85   $257.85   $257.90  
  Purchase #4 $148.71   5.502%   $156.892   $156.89   $156.90   $156.90  
  Purchase #5 $193.86   4.354%   $202.3007   $202.30   $202.30   $202.30  
  Purchase #6 $193.88   13.155%   $219.3849   $219.38   $219.40   $219.40  
  Purchase #7 $145.54   11.633%   $162.4707   $162.47   $162.45   $162.50  
  7 purchase totals = $1,230.30       $1,329.1535   $1,329.14   $1,329.15   $1,329.20