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 $208.46   6.566%   $222.1475   $222.15   $222.15   $222.10  
  Purchase #2 $44.47   5.278%   $46.8171   $46.82   $46.80   $46.80  
  Purchase #3 $250.89   4.509%   $262.2026   $262.20   $262.20   $262.20  
  Purchase #4 $249.30   11.361%   $277.623   $277.62   $277.60   $277.60  
  Purchase #5 $59.85   9.391%   $65.4705   $65.47   $65.45   $65.50  
  Purchase #6 $245.76   6.139%   $260.8472   $260.85   $260.85   $260.80  
  Purchase #7 $38.35   9.397%   $41.9537   $41.95   $41.95   $42.00  
  7 purchase totals = $1,097.08       $1,177.0616   $1,177.06   $1,177.00   $1,177.00