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 $93.86   3.137%   $96.8044   $96.80   $96.80   $96.80  
  Purchase #2 $13.58   4.239%   $14.1557   $14.16   $14.15   $14.20  
  Purchase #3 $66.56   10.280%   $73.4024   $73.40   $73.40   $73.40  
  Purchase #4 $194.81   12.189%   $218.5554   $218.56   $218.55   $218.60  
  Purchase #5 $169.26   10.815%   $187.5655   $187.57   $187.55   $187.60  
  Purchase #6 $223.32   11.225%   $248.3877   $248.39   $248.40   $248.40  
  Purchase #7 $23.74   11.147%   $26.3863   $26.39   $26.40   $26.40  
  7 purchase totals = $785.13       $865.2574   $865.27   $865.25   $865.40