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 $63.25   10.188%   $69.6939   $69.69   $69.70   $69.70  
  Purchase #2 $126.81   8.397%   $137.4582   $137.46   $137.45   $137.50  
  Purchase #3 $179.64   3.722%   $186.3262   $186.33   $186.35   $186.30  
  Purchase #4 $224.36   5.534%   $236.7761   $236.78   $236.80   $236.80  
  Purchase #5 $205.83   3.794%   $213.6392   $213.64   $213.65   $213.60  
  Purchase #6 $150.89   6.316%   $160.4202   $160.42   $160.40   $160.40  
  Purchase #7 $41.86   3.119%   $43.1656   $43.17   $43.15   $43.20  
  7 purchase totals = $992.64       $1,047.4794   $1,047.49   $1,047.50   $1,047.50