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 $26.26   12.602%   $29.5693   $29.57   $29.55   $29.60  
  Purchase #2 $167.75   7.154%   $179.7508   $179.75   $179.75   $179.80  
  Purchase #3 $91.67   6.536%   $97.6616   $97.66   $97.65   $97.70  
  Purchase #4 $114.53   10.381%   $126.4194   $126.42   $126.40   $126.40  
  Purchase #5 $207.67   10.135%   $228.7174   $228.72   $228.70   $228.70  
  Purchase #6 $95.54   8.291%   $103.4612   $103.46   $103.45   $103.50  
  Purchase #7 $248.69   5.496%   $262.358   $262.36   $262.35   $262.40  
  7 purchase totals = $952.11       $1,027.9377   $1,027.94   $1,027.85   $1,028.10