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 $79.28   11.177%   $88.1411   $88.14   $88.15   $88.10  
  Purchase #2 $92.28   6.844%   $98.5956   $98.60   $98.60   $98.60  
  Purchase #3 $193.32   11.684%   $215.9075   $215.91   $215.90   $215.90  
  Purchase #4 $207.52   6.612%   $221.2412   $221.24   $221.25   $221.20  
  Purchase #5 $47.44   8.229%   $51.3438   $51.34   $51.35   $51.30  
  Purchase #6 $205.66   8.174%   $222.4706   $222.47   $222.45   $222.50  
  Purchase #7 $234.48   12.387%   $263.525   $263.53   $263.55   $263.50  
  7 purchase totals = $1,059.98       $1,161.2248   $1,161.23   $1,161.25   $1,161.10