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 $242.43   10.138%   $267.0076   $267.01   $267.00   $267.00  
  Purchase #2 $198.82   6.536%   $211.8149   $211.81   $211.80   $211.80  
  Purchase #3 $116.58   8.726%   $126.7528   $126.75   $126.75   $126.80  
  Purchase #4 $202.93   4.277%   $211.6093   $211.61   $211.60   $211.60  
  Purchase #5 $102.94   11.411%   $114.6865   $114.69   $114.70   $114.70  
  Purchase #6 $161.33   3.859%   $167.5557   $167.56   $167.55   $167.60  
  Purchase #7 $217.76   13.444%   $247.0357   $247.04   $247.05   $247.00  
  7 purchase totals = $1,242.79       $1,346.4625   $1,346.47   $1,346.45   $1,346.50