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 $85.58   9.730%   $93.9069   $93.91   $93.90   $93.90  
  Purchase #2 $24.37   10.322%   $26.8855   $26.89   $26.90   $26.90  
  Purchase #3 $6.92   10.167%   $7.6236   $7.62   $7.60   $7.60  
  Purchase #4 $224.61   8.425%   $243.5334   $243.53   $243.55   $243.50  
  Purchase #5 $157.88   10.604%   $174.6216   $174.62   $174.60   $174.60  
  Purchase #6 $142.95   5.235%   $150.4334   $150.43   $150.45   $150.40  
  Purchase #7 $154.77   4.468%   $161.6851   $161.69   $161.70   $161.70  
  7 purchase totals = $797.08       $858.6895   $858.69   $858.70   $858.60