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 $155.54   13.477%   $176.5021   $176.50   $176.50   $176.50  
  Purchase #2 $87.87   10.141%   $96.7809   $96.78   $96.80   $96.80  
  Purchase #3 $86.51   12.740%   $97.5314   $97.53   $97.55   $97.50  
  Purchase #4 $78.80   7.403%   $84.6336   $84.63   $84.65   $84.60  
  Purchase #5 $61.42   9.545%   $67.2825   $67.28   $67.30   $67.30  
  Purchase #6 $154.50   6.182%   $164.0512   $164.05   $164.05   $164.10  
  Purchase #7 $65.95   7.431%   $70.8507   $70.85   $70.85   $70.90  
  7 purchase totals = $690.59       $757.6324   $757.62   $757.70   $757.70