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 $151.77   12.601%   $170.8945   $170.89   $170.90   $170.90  
  Purchase #2 $202.82   4.147%   $211.2309   $211.23   $211.25   $211.20  
  Purchase #3 $44.38   4.732%   $46.4801   $46.48   $46.50   $46.50  
  Purchase #4 $206.38   3.653%   $213.9191   $213.92   $213.90   $213.90  
  Purchase #5 $143.41   5.543%   $151.3592   $151.36   $151.35   $151.40  
  Purchase #6 $177.70   8.199%   $192.2696   $192.27   $192.25   $192.30  
  Purchase #7 $175.50   3.563%   $181.7531   $181.75   $181.75   $181.80  
  7 purchase totals = $1,101.96       $1,167.9065   $1,167.90   $1,167.90   $1,168.00