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 $38.71   10.513%   $42.7796   $42.78   $42.80   $42.80  
  Purchase #2 $177.58   9.555%   $194.5478   $194.55   $194.55   $194.50  
  Purchase #3 $250.61   4.675%   $262.326   $262.33   $262.35   $262.30  
  Purchase #4 $63.41   7.214%   $67.9844   $67.98   $68.00   $68.00  
  Purchase #5 $239.53   5.467%   $252.6251   $252.63   $252.65   $252.60  
  Purchase #6 $98.66   13.795%   $112.2701   $112.27   $112.25   $112.30  
  Purchase #7 $57.73   6.602%   $61.5413   $61.54   $61.55   $61.50  
  7 purchase totals = $926.23       $994.0743   $994.08   $994.15   $994.00