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 $206.84   12.462%   $232.6164   $232.62   $232.60   $232.60  
  Purchase #2 $208.88   7.461%   $224.4645   $224.46   $224.45   $224.50  
  Purchase #3 $67.67   5.199%   $71.1882   $71.19   $71.20   $71.20  
  Purchase #4 $205.96   5.335%   $216.948   $216.95   $216.95   $216.90  
  Purchase #5 $54.26   13.704%   $61.6958   $61.70   $61.70   $61.70  
  Purchase #6 $144.54   11.496%   $161.1563   $161.16   $161.15   $161.20  
  Purchase #7 $239.82   6.540%   $255.5042   $255.50   $255.50   $255.50  
  7 purchase totals = $1,127.97       $1,223.5734   $1,223.58   $1,223.55   $1,223.60