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 $44.76   6.394%   $47.622   $47.62   $47.60   $47.60  
  Purchase #2 $242.59   5.505%   $255.9446   $255.94   $255.95   $255.90  
  Purchase #3 $128.52   10.524%   $142.0454   $142.05   $142.05   $142.00  
  Purchase #4 $115.82   11.792%   $129.4775   $129.48   $129.50   $129.50  
  Purchase #5 $220.44   12.746%   $248.5373   $248.54   $248.55   $248.50  
  Purchase #6 $191.62   3.826%   $198.9514   $198.95   $198.95   $199.00  
  Purchase #7 $19.60   11.215%   $21.7981   $21.80   $21.80   $21.80  
  7 purchase totals = $963.35       $1,044.3763   $1,044.38   $1,044.40   $1,044.30