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 $237.64   12.692%   $267.8013   $267.80   $267.80   $267.80  
  Purchase #2 $119.42   6.368%   $127.0247   $127.02   $127.00   $127.00  
  Purchase #3 $185.93   6.553%   $198.114   $198.11   $198.10   $198.10  
  Purchase #4 $61.54   11.613%   $68.6866   $68.69   $68.70   $68.70  
  Purchase #5 $103.42   9.709%   $113.461   $113.46   $113.45   $113.50  
  Purchase #6 $206.65   11.595%   $230.6111   $230.61   $230.60   $230.60  
  Purchase #7 $64.58   8.746%   $70.2282   $70.23   $70.25   $70.20  
  7 purchase totals = $979.18       $1,075.9269   $1,075.92   $1,075.90   $1,075.90