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 $248.95   6.698%   $265.6247   $265.62   $265.60   $265.60  
  Purchase #2 $119.65   13.589%   $135.9092   $135.91   $135.90   $135.90  
  Purchase #3 $106.86   5.560%   $112.8014   $112.80   $112.80   $112.80  
  Purchase #4 $168.95   10.542%   $186.7607   $186.76   $186.75   $186.80  
  Purchase #5 $68.54   13.656%   $77.8998   $77.90   $77.90   $77.90  
  Purchase #6 $134.49   9.567%   $147.3567   $147.36   $147.35   $147.40  
  Purchase #7 $162.79   8.819%   $177.1465   $177.15   $177.15   $177.10  
  7 purchase totals = $1,010.23       $1,103.4990   $1,103.50   $1,103.45   $1,103.50