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 $85.82   12.110%   $96.2128   $96.21   $96.20   $96.20  
  Purchase #2 $16.61   13.576%   $18.865   $18.87   $18.85   $18.90  
  Purchase #3 $144.51   8.137%   $156.2688   $156.27   $156.25   $156.30  
  Purchase #4 $141.38   8.414%   $153.2757   $153.28   $153.30   $153.30  
  Purchase #5 $226.64   10.612%   $250.691   $250.69   $250.70   $250.70  
  Purchase #6 $108.72   4.481%   $113.5917   $113.59   $113.60   $113.60  
  Purchase #7 $58.25   9.386%   $63.7173   $63.72   $63.70   $63.70  
  7 purchase totals = $781.93       $852.6223   $852.63   $852.60   $852.70