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 $27.73   5.497%   $29.2543   $29.25   $29.25   $29.30  
  Purchase #2 $200.53   3.715%   $207.9797   $207.98   $208.00   $208.00  
  Purchase #3 $33.26   4.621%   $34.7969   $34.80   $34.80   $34.80  
  Purchase #4 $166.48   9.345%   $182.0376   $182.04   $182.05   $182.00  
  Purchase #5 $162.35   12.767%   $183.0772   $183.08   $183.10   $183.10  
  Purchase #6 $229.62   9.853%   $252.2445   $252.24   $252.25   $252.20  
  Purchase #7 $149.69   5.226%   $157.5128   $157.51   $157.50   $157.50  
  7 purchase totals = $969.66       $1,046.9030   $1,046.90   $1,046.95   $1,046.90