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 $36.81   13.686%   $41.8478   $41.85   $41.85   $41.80  
  Purchase #2 $235.30   6.541%   $250.691   $250.69   $250.70   $250.70  
  Purchase #3 $52.82   4.297%   $55.0897   $55.09   $55.10   $55.10  
  Purchase #4 $168.33   9.671%   $184.6092   $184.61   $184.60   $184.60  
  Purchase #5 $41.83   9.388%   $45.757   $45.76   $45.75   $45.80  
  Purchase #6 $145.53   6.509%   $155.0025   $155.00   $155.00   $155.00  
  Purchase #7 $182.54   6.267%   $193.9798   $193.98   $194.00   $194.00  
  7 purchase totals = $863.16       $926.9770   $926.98   $927.00   $927.00