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 $169.30   10.178%   $186.5314   $186.53   $186.55   $186.50  
  Purchase #2 $73.62   8.247%   $79.6914   $79.69   $79.70   $79.70  
  Purchase #3 $87.81   8.374%   $95.1632   $95.16   $95.15   $95.20  
  Purchase #4 $176.60   9.673%   $193.6825   $193.68   $193.70   $193.70  
  Purchase #5 $65.68   11.860%   $73.4696   $73.47   $73.45   $73.50  
  Purchase #6 $26.71   3.308%   $27.5936   $27.59   $27.60   $27.60  
  Purchase #7 $28.69   6.377%   $30.5196   $30.52   $30.50   $30.50  
  7 purchase totals = $628.41       $686.6513   $686.64   $686.65   $686.70