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 $39.55   9.827%   $43.4366   $43.44   $43.45   $43.40  
  Purchase #2 $107.68   10.699%   $119.2007   $119.20   $119.20   $119.20  
  Purchase #3 $99.66   10.144%   $109.7695   $109.77   $109.75   $109.80  
  Purchase #4 $23.48   11.186%   $26.1065   $26.11   $26.10   $26.10  
  Purchase #5 $235.40   3.823%   $244.3993   $244.40   $244.40   $244.40  
  Purchase #6 $200.72   10.425%   $221.6451   $221.65   $221.65   $221.60  
  Purchase #7 $199.70   6.780%   $213.2397   $213.24   $213.25   $213.20  
  7 purchase totals = $906.19       $977.7974   $977.81   $977.80   $977.70