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 $55.42   13.292%   $62.7864   $62.79   $62.80   $62.80  
  Purchase #2 $249.96   12.126%   $280.2701   $280.27   $280.25   $280.30  
  Purchase #3 $114.39   13.777%   $130.1495   $130.15   $130.15   $130.10  
  Purchase #4 $167.27   9.724%   $183.5353   $183.54   $183.55   $183.50  
  Purchase #5 $126.55   6.803%   $135.1592   $135.16   $135.15   $135.20  
  Purchase #6 $70.75   6.581%   $75.4061   $75.41   $75.40   $75.40  
  Purchase #7 $113.94   12.662%   $128.3671   $128.37   $128.35   $128.40  
  7 purchase totals = $898.28       $995.6737   $995.69   $995.65   $995.70