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 $196.66   10.868%   $218.033   $218.03   $218.05   $218.00  
  Purchase #2 $31.40   8.290%   $34.0031   $34.00   $34.00   $34.00  
  Purchase #3 $121.48   11.761%   $135.7673   $135.77   $135.75   $135.80  
  Purchase #4 $54.55   13.140%   $61.7179   $61.72   $61.70   $61.70  
  Purchase #5 $61.47   13.373%   $69.6904   $69.69   $69.70   $69.70  
  Purchase #6 $151.41   3.428%   $156.6003   $156.60   $156.60   $156.60  
  Purchase #7 $201.77   3.315%   $208.4587   $208.46   $208.45   $208.50  
  7 purchase totals = $818.74       $884.2707   $884.27   $884.25   $884.30