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 $49.63   13.593%   $56.3762   $56.38   $56.40   $56.40  
  Purchase #2 $231.82   6.161%   $246.1024   $246.10   $246.10   $246.10  
  Purchase #3 $122.47   11.805%   $136.9276   $136.93   $136.95   $136.90  
  Purchase #4 $59.68   13.678%   $67.843   $67.84   $67.85   $67.80  
  Purchase #5 $128.61   5.517%   $135.7054   $135.71   $135.70   $135.70  
  Purchase #6 $248.99   7.235%   $267.0044   $267.00   $267.00   $267.00  
  Purchase #7 $153.44   10.111%   $168.9543   $168.95   $168.95   $169.00  
  7 purchase totals = $994.64       $1,078.9133   $1,078.91   $1,078.95   $1,078.90