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 $208.79   8.314%   $226.1488   $226.15   $226.15   $226.10  
  Purchase #2 $97.76   6.219%   $103.8397   $103.84   $103.85   $103.80  
  Purchase #3 $58.76   8.342%   $63.6618   $63.66   $63.65   $63.70  
  Purchase #4 $188.79   10.445%   $208.5091   $208.51   $208.50   $208.50  
  Purchase #5 $81.96   4.158%   $85.3679   $85.37   $85.35   $85.40  
  Purchase #6 $147.35   3.273%   $152.1728   $152.17   $152.15   $152.20  
  Purchase #7 $184.58   4.147%   $192.2345   $192.23   $192.25   $192.20  
  7 purchase totals = $967.99       $1,031.9346   $1,031.93   $1,031.90   $1,031.90