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 $65.83   3.240%   $67.9629   $67.96   $67.95   $68.00  
  Purchase #2 $212.68   13.179%   $240.7091   $240.71   $240.70   $240.70  
  Purchase #3 $175.54   9.856%   $192.8412   $192.84   $192.85   $192.80  
  Purchase #4 $213.87   12.129%   $239.8103   $239.81   $239.80   $239.80  
  Purchase #5 $24.47   4.388%   $25.5437   $25.54   $25.55   $25.50  
  Purchase #6 $148.63   8.383%   $161.0897   $161.09   $161.10   $161.10  
  Purchase #7 $230.65   3.419%   $238.5359   $238.54   $238.55   $238.50  
  7 purchase totals = $1,071.67       $1,166.4928   $1,166.49   $1,166.50   $1,166.40