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 $61.68   3.682%   $63.9511   $63.95   $63.95   $64.00  
  Purchase #2 $65.35   8.749%   $71.0675   $71.07   $71.05   $71.10  
  Purchase #3 $113.35   10.115%   $124.8154   $124.82   $124.80   $124.80  
  Purchase #4 $162.37   6.708%   $173.2618   $173.26   $173.25   $173.30  
  Purchase #5 $74.44   13.518%   $84.5028   $84.50   $84.50   $84.50  
  Purchase #6 $83.65   6.625%   $89.1918   $89.19   $89.20   $89.20  
  Purchase #7 $69.25   4.847%   $72.6065   $72.61   $72.60   $72.60  
  7 purchase totals = $630.09       $679.3969   $679.40   $679.35   $679.50