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 $134.54   9.759%   $147.6698   $147.67   $147.65   $147.70  
  Purchase #2 $51.58   10.310%   $56.8979   $56.90   $56.90   $56.90  
  Purchase #3 $119.99   7.512%   $129.0036   $129.00   $129.00   $129.00  
  Purchase #4 $120.68   3.314%   $124.6793   $124.68   $124.70   $124.70  
  Purchase #5 $114.41   7.634%   $123.1441   $123.14   $123.15   $123.10  
  Purchase #6 $166.51   9.337%   $182.057   $182.06   $182.05   $182.10  
  Purchase #7 $119.71   11.226%   $133.1486   $133.15   $133.15   $133.10  
  7 purchase totals = $827.42       $896.6003   $896.60   $896.60   $896.60