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 $216.41   10.694%   $239.5529   $239.55   $239.55   $239.60  
  Purchase #2 $85.56   9.388%   $93.5924   $93.59   $93.60   $93.60  
  Purchase #3 $209.30   3.216%   $216.0311   $216.03   $216.05   $216.00  
  Purchase #4 $111.85   9.677%   $122.6737   $122.67   $122.65   $122.70  
  Purchase #5 $208.27   4.173%   $216.9611   $216.96   $216.95   $217.00  
  Purchase #6 $193.91   6.726%   $206.9524   $206.95   $206.95   $207.00  
  Purchase #7 $57.28   12.283%   $64.3157   $64.32   $64.30   $64.30  
  7 purchase totals = $1,082.58       $1,160.0793   $1,160.07   $1,160.05   $1,160.20