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 $61.28   12.581%   $68.9896   $68.99   $69.00   $69.00  
  Purchase #2 $234.32   11.871%   $262.1361   $262.14   $262.15   $262.10  
  Purchase #3 $42.60   11.831%   $47.64   $47.64   $47.65   $47.60  
  Purchase #4 $69.38   5.720%   $73.3485   $73.35   $73.35   $73.30  
  Purchase #5 $124.28   11.414%   $138.4653   $138.47   $138.45   $138.50  
  Purchase #6 $92.46   6.701%   $98.6557   $98.66   $98.65   $98.70  
  Purchase #7 $6.66   9.527%   $7.2945   $7.29   $7.30   $7.30  
  7 purchase totals = $630.98       $696.5297   $696.54   $696.55   $696.50