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 $208.58   11.321%   $232.1933   $232.19   $232.20   $232.20  
  Purchase #2 $34.93   6.870%   $37.3297   $37.33   $37.35   $37.30  
  Purchase #3 $242.44   12.496%   $272.7353   $272.74   $272.75   $272.70  
  Purchase #4 $51.99   13.563%   $59.0414   $59.04   $59.05   $59.00  
  Purchase #5 $37.28   12.419%   $41.9098   $41.91   $41.90   $41.90  
  Purchase #6 $27.61   4.633%   $28.8892   $28.89   $28.90   $28.90  
  Purchase #7 $231.95   7.348%   $248.9937   $248.99   $249.00   $249.00  
  7 purchase totals = $834.78       $921.0924   $921.09   $921.15   $921.00