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 $76.60   13.136%   $86.6622   $86.66   $86.65   $86.70  
  Purchase #2 $240.78   9.250%   $263.0522   $263.05   $263.05   $263.10  
  Purchase #3 $114.67   12.144%   $128.5955   $128.60   $128.60   $128.60  
  Purchase #4 $59.99   4.820%   $62.8815   $62.88   $62.90   $62.90  
  Purchase #5 $155.46   10.685%   $172.0709   $172.07   $172.05   $172.10  
  Purchase #6 $47.73   5.316%   $50.2673   $50.27   $50.25   $50.30  
  Purchase #7 $204.98   4.161%   $213.5092   $213.51   $213.50   $213.50  
  7 purchase totals = $900.21       $977.0388   $977.04   $977.00   $977.20