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 $15.94   10.678%   $17.6421   $17.64   $17.65   $17.60  
  Purchase #2 $86.96   11.175%   $96.6778   $96.68   $96.70   $96.70  
  Purchase #3 $21.95   11.826%   $24.5458   $24.55   $24.55   $24.50  
  Purchase #4 $232.53   12.501%   $261.5986   $261.60   $261.60   $261.60  
  Purchase #5 $118.79   5.382%   $125.1833   $125.18   $125.20   $125.20  
  Purchase #6 $5.45   3.763%   $5.6551   $5.66   $5.65   $5.70  
  Purchase #7 $153.32   9.523%   $167.9207   $167.92   $167.90   $167.90  
  7 purchase totals = $634.94       $699.2234   $699.23   $699.25   $699.20