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 $181.25   6.184%   $192.4585   $192.46   $192.45   $192.50  
  Purchase #2 $114.52   13.854%   $130.3856   $130.39   $130.40   $130.40  
  Purchase #3 $227.37   3.241%   $234.7391   $234.74   $234.75   $234.70  
  Purchase #4 $114.57   6.814%   $122.3768   $122.38   $122.40   $122.40  
  Purchase #5 $211.68   13.292%   $239.8165   $239.82   $239.80   $239.80  
  Purchase #6 $29.38   13.857%   $33.4512   $33.45   $33.45   $33.50  
  Purchase #7 $108.28   5.287%   $114.0048   $114.00   $114.00   $114.00  
  7 purchase totals = $987.05       $1,067.2325   $1,067.24   $1,067.25   $1,067.30