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 $68.84   8.462%   $74.6652   $74.67   $74.65   $74.70  
  Purchase #2 $179.78   5.509%   $189.6841   $189.68   $189.70   $189.70  
  Purchase #3 $189.75   6.426%   $201.9433   $201.94   $201.95   $201.90  
  Purchase #4 $58.57   8.725%   $63.6802   $63.68   $63.70   $63.70  
  Purchase #5 $177.55   8.122%   $191.9706   $191.97   $191.95   $192.00  
  Purchase #6 $49.66   8.303%   $53.7833   $53.78   $53.80   $53.80  
  Purchase #7 $172.40   4.461%   $180.0908   $180.09   $180.10   $180.10  
  7 purchase totals = $896.55       $955.8175   $955.81   $955.85   $955.90