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 $97.80   7.781%   $105.4098   $105.41   $105.40   $105.40  
  Purchase #2 $103.45   13.300%   $117.2089   $117.21   $117.20   $117.20  
  Purchase #3 $92.28   10.603%   $102.0644   $102.06   $102.05   $102.10  
  Purchase #4 $67.52   9.241%   $73.7595   $73.76   $73.75   $73.80  
  Purchase #5 $14.25   8.177%   $15.4152   $15.42   $15.40   $15.40  
  Purchase #6 $29.96   7.274%   $32.1393   $32.14   $32.15   $32.10  
  Purchase #7 $147.51   3.719%   $152.9959   $153.00   $153.00   $153.00  
  7 purchase totals = $552.77       $598.9930   $599.00   $598.95   $599.00