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 $63.66   4.509%   $66.5304   $66.53   $66.55   $66.50  
  Purchase #2 $17.56   7.398%   $18.8591   $18.86   $18.85   $18.90  
  Purchase #3 $87.28   11.357%   $97.1924   $97.19   $97.20   $97.20  
  Purchase #4 $236.58   4.872%   $248.1062   $248.11   $248.10   $248.10  
  Purchase #5 $22.64   10.576%   $25.0344   $25.03   $25.05   $25.00  
  Purchase #6 $200.91   5.311%   $211.5803   $211.58   $211.60   $211.60  
  Purchase #7 $95.76   4.233%   $99.8135   $99.81   $99.80   $99.80  
  7 purchase totals = $724.39       $767.1163   $767.11   $767.15   $767.10