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 $37.36   3.685%   $38.7367   $38.74   $38.75   $38.70  
  Purchase #2 $235.84   3.716%   $244.6038   $244.60   $244.60   $244.60  
  Purchase #3 $55.99   5.183%   $58.892   $58.89   $58.90   $58.90  
  Purchase #4 $75.25   4.343%   $78.5181   $78.52   $78.50   $78.50  
  Purchase #5 $55.84   13.111%   $63.1612   $63.16   $63.15   $63.20  
  Purchase #6 $172.59   5.632%   $182.3103   $182.31   $182.30   $182.30  
  Purchase #7 $182.66   8.825%   $198.7797   $198.78   $198.80   $198.80  
  7 purchase totals = $815.53       $865.0018   $865.00   $865.00   $865.00