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 $235.75   13.543%   $267.6776   $267.68   $267.70   $267.70  
  Purchase #2 $44.74   4.518%   $46.7614   $46.76   $46.75   $46.80  
  Purchase #3 $112.88   9.672%   $123.7978   $123.80   $123.80   $123.80  
  Purchase #4 $86.55   5.629%   $91.4219   $91.42   $91.40   $91.40  
  Purchase #5 $23.46   9.278%   $25.6366   $25.64   $25.65   $25.60  
  Purchase #6 $91.83   7.638%   $98.844   $98.84   $98.85   $98.80  
  Purchase #7 $81.76   10.559%   $90.393   $90.39   $90.40   $90.40  
  7 purchase totals = $676.97       $744.5323   $744.53   $744.55   $744.50