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 $184.36   12.798%   $207.9544   $207.95   $207.95   $208.00  
  Purchase #2 $182.50   13.518%   $207.1704   $207.17   $207.15   $207.20  
  Purchase #3 $26.58   13.717%   $30.226   $30.23   $30.25   $30.20  
  Purchase #4 $125.91   10.793%   $139.4995   $139.50   $139.50   $139.50  
  Purchase #5 $152.49   5.764%   $161.2795   $161.28   $161.30   $161.30  
  Purchase #6 $47.67   6.556%   $50.7952   $50.80   $50.80   $50.80  
  Purchase #7 $40.60   10.835%   $44.999   $45.00   $45.00   $45.00  
  7 purchase totals = $760.11       $841.9240   $841.93   $841.95   $842.00