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 $183.28   13.699%   $208.3875   $208.39   $208.40   $208.40  
  Purchase #2 $62.53   7.603%   $67.2842   $67.28   $67.30   $67.30  
  Purchase #3 $224.90   9.838%   $247.0257   $247.03   $247.05   $247.00  
  Purchase #4 $231.54   9.623%   $253.8211   $253.82   $253.80   $253.80  
  Purchase #5 $92.61   5.775%   $97.9582   $97.96   $97.95   $98.00  
  Purchase #6 $51.86   3.380%   $53.6129   $53.61   $53.60   $53.60  
  Purchase #7 $49.58   8.759%   $53.9227   $53.92   $53.90   $53.90  
  7 purchase totals = $896.30       $982.0123   $982.01   $982.00   $982.00