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 $24.48   7.856%   $26.4031   $26.40   $26.40   $26.40  
  Purchase #2 $63.60   11.116%   $70.6698   $70.67   $70.65   $70.70  
  Purchase #3 $59.86   13.723%   $68.0746   $68.07   $68.05   $68.10  
  Purchase #4 $180.99   6.623%   $192.977   $192.98   $193.00   $193.00  
  Purchase #5 $104.84   8.476%   $113.7262   $113.73   $113.75   $113.70  
  Purchase #6 $114.85   10.337%   $126.722   $126.72   $126.70   $126.70  
  Purchase #7 $192.59   7.365%   $206.7743   $206.77   $206.75   $206.80  
  7 purchase totals = $741.21       $805.3470   $805.34   $805.30   $805.40