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 $168.34   11.536%   $187.7597   $187.76   $187.75   $187.80  
  Purchase #2 $61.45   3.526%   $63.6167   $63.62   $63.60   $63.60  
  Purchase #3 $221.40   8.105%   $239.3445   $239.34   $239.35   $239.30  
  Purchase #4 $18.65   3.376%   $19.2796   $19.28   $19.30   $19.30  
  Purchase #5 $183.44   12.660%   $206.6635   $206.66   $206.65   $206.70  
  Purchase #6 $152.75   3.209%   $157.6517   $157.65   $157.65   $157.70  
  Purchase #7 $169.39   9.108%   $184.818   $184.82   $184.80   $184.80  
  7 purchase totals = $975.42       $1,059.1337   $1,059.13   $1,059.10   $1,059.20