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 $88.36   11.667%   $98.669   $98.67   $98.65   $98.70  
  Purchase #2 $226.89   4.247%   $236.526   $236.53   $236.55   $236.50  
  Purchase #3 $196.99   7.520%   $211.8036   $211.80   $211.80   $211.80  
  Purchase #4 $102.90   11.691%   $114.93   $114.93   $114.95   $114.90  
  Purchase #5 $89.38   7.792%   $96.3445   $96.34   $96.35   $96.30  
  Purchase #6 $50.75   8.387%   $55.0064   $55.01   $55.00   $55.00  
  Purchase #7 $26.28   10.202%   $28.9611   $28.96   $28.95   $29.00  
  7 purchase totals = $781.55       $842.2406   $842.24   $842.25   $842.20