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 $46.93   13.268%   $53.1567   $53.16   $53.15   $53.20  
  Purchase #2 $216.51   8.697%   $235.3399   $235.34   $235.35   $235.30  
  Purchase #3 $115.55   11.665%   $129.0289   $129.03   $129.05   $129.00  
  Purchase #4 $91.38   4.826%   $95.79   $95.79   $95.80   $95.80  
  Purchase #5 $114.26   11.329%   $127.2045   $127.20   $127.20   $127.20  
  Purchase #6 $87.95   8.237%   $95.1944   $95.19   $95.20   $95.20  
  Purchase #7 $206.50   8.502%   $224.0566   $224.06   $224.05   $224.10  
  7 purchase totals = $879.08       $959.7710   $959.77   $959.80   $959.80