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 $65.40   12.793%   $73.7666   $73.77   $73.75   $73.80  
  Purchase #2 $224.54   10.486%   $248.0853   $248.09   $248.10   $248.10  
  Purchase #3 $111.74   4.268%   $116.5091   $116.51   $116.50   $116.50  
  Purchase #4 $51.48   3.462%   $53.2622   $53.26   $53.25   $53.30  
  Purchase #5 $24.96   6.766%   $26.6488   $26.65   $26.65   $26.60  
  Purchase #6 $243.69   9.229%   $266.1802   $266.18   $266.20   $266.20  
  Purchase #7 $123.49   3.163%   $127.396   $127.40   $127.40   $127.40  
  7 purchase totals = $845.30       $911.8482   $911.86   $911.85   $911.90