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 $221.26   11.254%   $246.1606   $246.16   $246.15   $246.20  
  Purchase #2 $117.31   8.749%   $127.5735   $127.57   $127.55   $127.60  
  Purchase #3 $248.81   5.334%   $262.0815   $262.08   $262.10   $262.10  
  Purchase #4 $124.42   13.229%   $140.8795   $140.88   $140.90   $140.90  
  Purchase #5 $185.75   3.512%   $192.2735   $192.27   $192.25   $192.30  
  Purchase #6 $177.68   10.399%   $196.1569   $196.16   $196.15   $196.20  
  Purchase #7 $232.85   13.669%   $264.6783   $264.68   $264.70   $264.70  
  7 purchase totals = $1,308.08       $1,429.8038   $1,429.80   $1,429.80   $1,430.00