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 $58.36   12.553%   $65.6859   $65.69   $65.70   $65.70  
  Purchase #2 $72.83   11.315%   $81.0707   $81.07   $81.05   $81.10  
  Purchase #3 $248.39   4.432%   $259.3986   $259.40   $259.40   $259.40  
  Purchase #4 $147.78   13.121%   $167.1702   $167.17   $167.15   $167.20  
  Purchase #5 $227.65   7.183%   $244.0021   $244.00   $244.00   $244.00  
  Purchase #6 $121.28   10.703%   $134.2606   $134.26   $134.25   $134.30  
  Purchase #7 $237.63   11.283%   $264.4418   $264.44   $264.45   $264.40  
  7 purchase totals = $1,113.92       $1,216.0299   $1,216.03   $1,216.00   $1,216.10