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 $101.42   10.145%   $111.7091   $111.71   $111.70   $111.70  
  Purchase #2 $195.28   13.312%   $221.2757   $221.28   $221.30   $221.30  
  Purchase #3 $44.64   8.182%   $48.2924   $48.29   $48.30   $48.30  
  Purchase #4 $115.51   3.706%   $119.7908   $119.79   $119.80   $119.80  
  Purchase #5 $221.35   6.150%   $234.963   $234.96   $234.95   $235.00  
  Purchase #6 $50.76   10.701%   $56.1918   $56.19   $56.20   $56.20  
  Purchase #7 $64.83   4.814%   $67.9509   $67.95   $67.95   $68.00  
  7 purchase totals = $793.79       $860.1737   $860.17   $860.20   $860.30