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 $59.65   7.273%   $63.9883   $63.99   $64.00   $64.00  
  Purchase #2 $211.74   13.502%   $240.3291   $240.33   $240.35   $240.30  
  Purchase #3 $215.40   8.423%   $233.5431   $233.54   $233.55   $233.50  
  Purchase #4 $200.62   9.833%   $220.347   $220.35   $220.35   $220.30  
  Purchase #5 $73.90   8.804%   $80.4062   $80.41   $80.40   $80.40  
  Purchase #6 $13.25   12.251%   $14.8733   $14.87   $14.85   $14.90  
  Purchase #7 $108.48   5.510%   $114.4572   $114.46   $114.45   $114.50  
  7 purchase totals = $883.04       $967.9442   $967.95   $967.95   $967.90