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 $84.81   13.419%   $96.1907   $96.19   $96.20   $96.20  
  Purchase #2 $248.95   4.261%   $259.5578   $259.56   $259.55   $259.60  
  Purchase #3 $176.47   9.648%   $193.4958   $193.50   $193.50   $193.50  
  Purchase #4 $11.35   11.269%   $12.629   $12.63   $12.65   $12.60  
  Purchase #5 $34.80   11.604%   $38.8382   $38.84   $38.85   $38.80  
  Purchase #6 $196.85   4.838%   $206.3736   $206.37   $206.35   $206.40  
  Purchase #7 $44.40   10.282%   $48.9652   $48.97   $48.95   $49.00  
  7 purchase totals = $797.63       $856.0503   $856.06   $856.05   $856.10