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 $8.37   9.394%   $9.1563   $9.16   $9.15   $9.20  
  Purchase #2 $33.32   9.516%   $36.4907   $36.49   $36.50   $36.50  
  Purchase #3 $103.67   4.873%   $108.7218   $108.72   $108.70   $108.70  
  Purchase #4 $53.28   6.821%   $56.9142   $56.91   $56.90   $56.90  
  Purchase #5 $79.55   6.312%   $84.5712   $84.57   $84.55   $84.60  
  Purchase #6 $28.94   3.443%   $29.9364   $29.94   $29.95   $29.90  
  Purchase #7 $82.73   3.458%   $85.5908   $85.59   $85.60   $85.60  
  7 purchase totals = $389.86       $411.3814   $411.38   $411.35   $411.40