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 $61.50   8.285%   $66.5953   $66.60   $66.60   $66.60  
  Purchase #2 $154.36   11.783%   $172.5482   $172.55   $172.55   $172.50  
  Purchase #3 $184.72   12.543%   $207.8894   $207.89   $207.90   $207.90  
  Purchase #4 $243.29   10.704%   $269.3318   $269.33   $269.35   $269.30  
  Purchase #5 $72.60   5.211%   $76.3832   $76.38   $76.40   $76.40  
  Purchase #6 $168.63   8.572%   $183.085   $183.09   $183.10   $183.10  
  Purchase #7 $84.26   12.839%   $95.0781   $95.08   $95.10   $95.10  
  7 purchase totals = $969.36       $1,070.9110   $1,070.92   $1,071.00   $1,070.90