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 $55.97   12.782%   $63.1241   $63.12   $63.10   $63.10  
  Purchase #2 $94.28   4.317%   $98.3501   $98.35   $98.35   $98.40  
  Purchase #3 $99.54   11.196%   $110.6845   $110.68   $110.70   $110.70  
  Purchase #4 $74.61   6.393%   $79.3798   $79.38   $79.40   $79.40  
  Purchase #5 $32.25   11.182%   $35.8562   $35.86   $35.85   $35.90  
  Purchase #6 $44.34   5.835%   $46.9272   $46.93   $46.95   $46.90  
  Purchase #7 $235.49   5.671%   $248.8446   $248.84   $248.85   $248.80  
  7 purchase totals = $636.48       $683.1665   $683.16   $683.20   $683.20