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 $24.99   5.476%   $26.3585   $26.36   $26.35   $26.40  
  Purchase #2 $183.80   6.656%   $196.0337   $196.03   $196.05   $196.00  
  Purchase #3 $237.37   10.857%   $263.1413   $263.14   $263.15   $263.10  
  Purchase #4 $159.72   13.116%   $180.6689   $180.67   $180.65   $180.70  
  Purchase #5 $35.56   10.794%   $39.3983   $39.40   $39.40   $39.40  
  Purchase #6 $127.91   10.166%   $140.9133   $140.91   $140.90   $140.90  
  Purchase #7 $211.91   7.840%   $228.5237   $228.52   $228.50   $228.50  
  7 purchase totals = $981.26       $1,075.0377   $1,075.03   $1,075.00   $1,075.00