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 $88.55   11.280%   $98.5384   $98.54   $98.55   $98.50  
  Purchase #2 $23.58   13.176%   $26.6869   $26.69   $26.70   $26.70  
  Purchase #3 $74.37   12.420%   $83.6068   $83.61   $83.60   $83.60  
  Purchase #4 $148.78   13.738%   $169.2194   $169.22   $169.20   $169.20  
  Purchase #5 $215.93   8.640%   $234.5864   $234.59   $234.60   $234.60  
  Purchase #6 $67.29   4.432%   $70.2723   $70.27   $70.25   $70.30  
  Purchase #7 $43.45   12.461%   $48.8643   $48.86   $48.85   $48.90  
  7 purchase totals = $661.95       $731.7745   $731.78   $731.75   $731.80