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 $233.62   13.868%   $266.0184   $266.02   $266.00   $266.00  
  Purchase #2 $50.81   3.416%   $52.5457   $52.55   $52.55   $52.50  
  Purchase #3 $246.65   12.777%   $278.1645   $278.16   $278.15   $278.20  
  Purchase #4 $232.73   13.693%   $264.5977   $264.60   $264.60   $264.60  
  Purchase #5 $16.86   4.363%   $17.5956   $17.60   $17.60   $17.60  
  Purchase #6 $134.91   10.399%   $148.9393   $148.94   $148.95   $148.90  
  Purchase #7 $248.94   11.115%   $276.6097   $276.61   $276.60   $276.60  
  7 purchase totals = $1,164.52       $1,304.4709   $1,304.48   $1,304.45   $1,304.40