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 $122.61   9.419%   $134.1586   $134.16   $134.15   $134.20  
  Purchase #2 $52.34   10.173%   $57.6645   $57.66   $57.65   $57.70  
  Purchase #3 $54.61   13.630%   $62.0533   $62.05   $62.05   $62.10  
  Purchase #4 $198.31   4.649%   $207.5294   $207.53   $207.55   $207.50  
  Purchase #5 $113.34   4.585%   $118.5366   $118.54   $118.55   $118.50  
  Purchase #6 $191.99   11.156%   $213.4084   $213.41   $213.40   $213.40  
  Purchase #7 $67.62   10.562%   $74.762   $74.76   $74.75   $74.80  
  7 purchase totals = $800.82       $868.1128   $868.11   $868.10   $868.20