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 $61.63   5.659%   $65.1176   $65.12   $65.10   $65.10  
  Purchase #2 $250.35   10.247%   $276.0034   $276.00   $276.00   $276.00  
  Purchase #3 $152.80   13.447%   $173.347   $173.35   $173.35   $173.30  
  Purchase #4 $114.75   8.456%   $124.4533   $124.45   $124.45   $124.50  
  Purchase #5 $201.76   9.797%   $221.5264   $221.53   $221.55   $221.50  
  Purchase #6 $77.65   8.242%   $84.0499   $84.05   $84.05   $84.00  
  Purchase #7 $22.49   3.188%   $23.207   $23.21   $23.20   $23.20  
  7 purchase totals = $881.43       $967.7046   $967.71   $967.70   $967.60