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 $223.35   11.207%   $248.3808   $248.38   $248.40   $248.40  
  Purchase #2 $180.73   9.391%   $197.7024   $197.70   $197.70   $197.70  
  Purchase #3 $229.86   8.798%   $250.0831   $250.08   $250.10   $250.10  
  Purchase #4 $166.45   6.483%   $177.241   $177.24   $177.25   $177.20  
  Purchase #5 $113.56   9.114%   $123.9099   $123.91   $123.90   $123.90  
  Purchase #6 $120.83   11.339%   $134.5309   $134.53   $134.55   $134.50  
  Purchase #7 $172.34   11.835%   $192.7364   $192.74   $192.75   $192.70  
  7 purchase totals = $1,207.12       $1,324.5845   $1,324.58   $1,324.65   $1,324.50