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 $76.98   3.571%   $79.729   $79.73   $79.75   $79.70  
  Purchase #2 $85.77   13.526%   $97.3713   $97.37   $97.35   $97.40  
  Purchase #3 $89.98   5.602%   $95.0207   $95.02   $95.00   $95.00  
  Purchase #4 $14.32   7.483%   $15.3916   $15.39   $15.40   $15.40  
  Purchase #5 $239.80   3.799%   $248.91   $248.91   $248.90   $248.90  
  Purchase #6 $155.54   12.498%   $174.9794   $174.98   $175.00   $175.00  
  Purchase #7 $77.35   10.136%   $85.1902   $85.19   $85.20   $85.20  
  7 purchase totals = $739.74       $796.5922   $796.59   $796.60   $796.60