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 $86.70   11.860%   $96.9826   $96.98   $97.00   $97.00  
  Purchase #2 $63.61   4.862%   $66.7027   $66.70   $66.70   $66.70  
  Purchase #3 $229.96   5.619%   $242.8815   $242.88   $242.90   $242.90  
  Purchase #4 $53.36   10.458%   $58.9404   $58.94   $58.95   $58.90  
  Purchase #5 $167.96   9.527%   $183.9615   $183.96   $183.95   $184.00  
  Purchase #6 $188.92   10.333%   $208.4411   $208.44   $208.45   $208.40  
  Purchase #7 $50.77   5.659%   $53.6431   $53.64   $53.65   $53.60  
  7 purchase totals = $841.28       $911.5529   $911.54   $911.60   $911.50