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 $61.70   6.197%   $65.5235   $65.52   $65.50   $65.50  
  Purchase #2 $54.94   9.829%   $60.3401   $60.34   $60.35   $60.30  
  Purchase #3 $98.44   6.238%   $104.5807   $104.58   $104.60   $104.60  
  Purchase #4 $103.38   8.693%   $112.3668   $112.37   $112.35   $112.40  
  Purchase #5 $192.29   8.307%   $208.2635   $208.26   $208.25   $208.30  
  Purchase #6 $166.76   9.638%   $182.8323   $182.83   $182.85   $182.80  
  Purchase #7 $60.38   5.357%   $63.6146   $63.61   $63.60   $63.60  
  7 purchase totals = $737.89       $797.5215   $797.51   $797.50   $797.50