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 $232.63   10.145%   $256.2303   $256.23   $256.25   $256.20  
  Purchase #2 $231.63   7.227%   $248.3699   $248.37   $248.35   $248.40  
  Purchase #3 $174.44   4.685%   $182.6125   $182.61   $182.60   $182.60  
  Purchase #4 $33.82   3.717%   $35.0771   $35.08   $35.10   $35.10  
  Purchase #5 $234.44   3.827%   $243.412   $243.41   $243.40   $243.40  
  Purchase #6 $214.63   11.795%   $239.9456   $239.95   $239.95   $239.90  
  Purchase #7 $157.72   3.261%   $162.8632   $162.86   $162.85   $162.90  
  7 purchase totals = $1,279.31       $1,368.5106   $1,368.51   $1,368.50   $1,368.50