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 $214.43   9.142%   $234.0332   $234.03   $234.05   $234.00  
  Purchase #2 $52.69   10.543%   $58.2451   $58.25   $58.25   $58.20  
  Purchase #3 $157.41   6.138%   $167.0718   $167.07   $167.05   $167.10  
  Purchase #4 $211.66   3.226%   $218.4882   $218.49   $218.50   $218.50  
  Purchase #5 $34.75   11.109%   $38.6104   $38.61   $38.60   $38.60  
  Purchase #6 $71.94   13.237%   $81.4627   $81.46   $81.45   $81.50  
  Purchase #7 $106.84   8.184%   $115.5838   $115.58   $115.60   $115.60  
  7 purchase totals = $849.72       $913.4952   $913.49   $913.50   $913.50