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 $181.29   7.711%   $195.2693   $195.27   $195.25   $195.30  
  Purchase #2 $107.33   6.231%   $114.0177   $114.02   $114.00   $114.00  
  Purchase #3 $71.71   10.620%   $79.3256   $79.33   $79.35   $79.30  
  Purchase #4 $33.99   4.629%   $35.5634   $35.56   $35.55   $35.60  
  Purchase #5 $207.35   7.189%   $222.2564   $222.26   $222.25   $222.30  
  Purchase #6 $137.47   6.303%   $146.1347   $146.13   $146.15   $146.10  
  Purchase #7 $37.34   8.174%   $40.3922   $40.39   $40.40   $40.40  
  7 purchase totals = $776.48       $832.9593   $832.96   $832.95   $833.00