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 $22.89   13.612%   $26.0058   $26.01   $26.00   $26.00  
  Purchase #2 $156.70   4.415%   $163.6183   $163.62   $163.60   $163.60  
  Purchase #3 $171.58   13.487%   $194.721   $194.72   $194.70   $194.70  
  Purchase #4 $220.60   12.759%   $248.7464   $248.75   $248.75   $248.70  
  Purchase #5 $155.47   5.668%   $164.282   $164.28   $164.30   $164.30  
  Purchase #6 $18.39   4.256%   $19.1727   $19.17   $19.15   $19.20  
  Purchase #7 $83.66   5.219%   $88.0262   $88.03   $88.05   $88.00  
  7 purchase totals = $829.29       $904.5724   $904.58   $904.55   $904.50