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 $95.34   3.725%   $98.8914   $98.89   $98.90   $98.90  
  Purchase #2 $105.56   8.612%   $114.6508   $114.65   $114.65   $114.70  
  Purchase #3 $71.38   4.809%   $74.8127   $74.81   $74.80   $74.80  
  Purchase #4 $26.36   6.823%   $28.1585   $28.16   $28.15   $28.20  
  Purchase #5 $5.98   4.425%   $6.2446   $6.24   $6.25   $6.20  
  Purchase #6 $186.36   10.873%   $206.6229   $206.62   $206.60   $206.60  
  Purchase #7 $110.85   9.467%   $121.3442   $121.34   $121.35   $121.30  
  7 purchase totals = $601.83       $650.7251   $650.71   $650.70   $650.70