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 $85.95   9.308%   $93.9502   $93.95   $93.95   $94.00  
  Purchase #2 $46.55   6.379%   $49.5194   $49.52   $49.50   $49.50  
  Purchase #3 $115.71   4.793%   $121.256   $121.26   $121.25   $121.30  
  Purchase #4 $118.28   8.212%   $127.9932   $127.99   $128.00   $128.00  
  Purchase #5 $81.90   12.223%   $91.9106   $91.91   $91.90   $91.90  
  Purchase #6 $105.83   8.754%   $115.0944   $115.09   $115.10   $115.10  
  Purchase #7 $74.50   5.655%   $78.713   $78.71   $78.70   $78.70  
  7 purchase totals = $628.72       $678.4368   $678.43   $678.40   $678.50