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 $89.60   6.191%   $95.1471   $95.15   $95.15   $95.10  
  Purchase #2 $43.29   10.130%   $47.6753   $47.68   $47.70   $47.70  
  Purchase #3 $95.26   6.737%   $101.6777   $101.68   $101.70   $101.70  
  Purchase #4 $158.33   4.595%   $165.6053   $165.61   $165.60   $165.60  
  Purchase #5 $34.36   6.463%   $36.5807   $36.58   $36.60   $36.60  
  Purchase #6 $27.81   10.177%   $30.6402   $30.64   $30.65   $30.60  
  Purchase #7 $217.47   5.684%   $229.831   $229.83   $229.85   $229.80  
  7 purchase totals = $666.12       $707.1573   $707.17   $707.25   $707.10