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 $207.35   11.193%   $230.5587   $230.56   $230.55   $230.60  
  Purchase #2 $182.81   10.149%   $201.3634   $201.36   $201.35   $201.40  
  Purchase #3 $114.60   8.780%   $124.6619   $124.66   $124.65   $124.70  
  Purchase #4 $146.91   13.839%   $167.2409   $167.24   $167.25   $167.20  
  Purchase #5 $105.31   3.223%   $108.7041   $108.70   $108.70   $108.70  
  Purchase #6 $57.25   4.793%   $59.994   $59.99   $60.00   $60.00  
  Purchase #7 $79.42   9.553%   $87.007   $87.01   $87.00   $87.00  
  7 purchase totals = $893.65       $979.5300   $979.52   $979.50   $979.60