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 $73.42   5.730%   $77.627   $77.63   $77.65   $77.60  
  Purchase #2 $45.97   4.188%   $47.8952   $47.90   $47.90   $47.90  
  Purchase #3 $95.69   13.115%   $108.2397   $108.24   $108.25   $108.20  
  Purchase #4 $49.28   13.152%   $55.7613   $55.76   $55.75   $55.80  
  Purchase #5 $174.68   12.405%   $196.3491   $196.35   $196.35   $196.30  
  Purchase #6 $64.82   5.470%   $68.3657   $68.37   $68.35   $68.40  
  Purchase #7 $155.62   8.831%   $169.3628   $169.36   $169.35   $169.40  
  7 purchase totals = $659.48       $723.6008   $723.61   $723.60   $723.60