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 $106.62   6.361%   $113.4021   $113.40   $113.40   $113.40  
  Purchase #2 $178.27   6.213%   $189.3459   $189.35   $189.35   $189.30  
  Purchase #3 $23.81   10.795%   $26.3803   $26.38   $26.40   $26.40  
  Purchase #4 $77.64   10.421%   $85.7309   $85.73   $85.75   $85.70  
  Purchase #5 $71.52   7.798%   $77.0971   $77.10   $77.10   $77.10  
  Purchase #6 $73.63   4.145%   $76.682   $76.68   $76.70   $76.70  
  Purchase #7 $156.58   13.600%   $177.8749   $177.87   $177.85   $177.90  
  7 purchase totals = $688.07       $746.5132   $746.51   $746.55   $746.50