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 $239.86   11.871%   $268.3338   $268.33   $268.35   $268.30  
  Purchase #2 $171.45   12.218%   $192.3978   $192.40   $192.40   $192.40  
  Purchase #3 $225.26   10.295%   $248.4505   $248.45   $248.45   $248.50  
  Purchase #4 $170.40   10.207%   $187.7927   $187.79   $187.80   $187.80  
  Purchase #5 $60.38   8.425%   $65.467   $65.47   $65.45   $65.50  
  Purchase #6 $35.77   7.714%   $38.5293   $38.53   $38.55   $38.50  
  Purchase #7 $185.65   5.715%   $196.2599   $196.26   $196.25   $196.30  
  7 purchase totals = $1,088.77       $1,197.2310   $1,197.23   $1,197.25   $1,197.30